Dictionary of Ichthyology
Brian W. Coad and Don E. McAllister†
O
O = Ordovician, a geological period within the Palaeozoic ca. 504-441 million years ago.
OA = the upper, ventro-lateral row of photophores running above the ventral series from just behind the operculum to above the anal fin.
Oannes = the foremost of the the fish men who brought civilisation to the Babylonians. Lived on land during the day but had to return to water at night. Had a human form but wore a cap resembling a fish head and a long fish-skin cape. Became the fish god Dagon later. See also Atargatis.
ob- (prefix) = toward, over, to, against, e.g. dorsal obbasal scales in Mugilidae are large modified scales at the dorsal fin origin.
objective synonym = each of two or more names with different spelling applied to one and the same taxon. Objective synonyms are the two or more synonyms used on the same type.
obligate = limited to; dependent on, e.g. Notropis hudsonius is an obligatory freshwater fish, not being capable of entering the sea. Opposite of facultative.
obligate lecithotrophic live bearer = a reproductive guild (q.v.) where eggs are fertilised internally and develop in the female until the end of the embryonic phase or later. There is no maternal-foetal nutrient transfer (yolk provides food). There is some specialisation for intrauterine respiration, excretion and osmoregulation. Weight decreases during embryonic development, e.g. Poecilia reticulata. See also facultative lecithotrophic live bearer.
obligate parasite = a parasite that cannot lead an independent existence. Compare facultative parasite.
obligatory = adjective for obligate.
oblique rows of scales = diagonal scale rows (the almost vertical rows of scales slanting backwards and downwards across the sides of the body. Divided into scales above the lateral line starting at the front of the dorsal fin (from, but not including, the scale in the mid-dorsal row, to but not including, the lateral line scales) and below the lateral line similarly ending at the front of the anal fin. The number of transverse rows themselves along the body may also be counted).
obliterative colouration = a graded colouration or shading that washes out relief, giving the appearance of a flat surface. Useful in concealing fish from predators.
observer = a government official/scientist onboard a fishing vessel who collects scientific information and measures harvest amounts to ensure that established catch levels are not exceeded. May also quantify bycatch and discards, and collect tagged fish.
obsolescent = almost wanting; minute.
obsolete = rudimentary, hardly developed, faintly marked.
obstruction = fastener (an obstruction on the sea floor that can foul and damage fishing gear).
obtuse = blunt, having an angle of more than 90 degrees.
Occam's razor = other things being equal, the simpler hypothesis is chosen. Also known as the Law of Parsimony.
occidental = western or westerly.
occipital = 1) a median bone on the upper surface of the back of the head.
occipital = 2) pertaining to the occiput.
occipital canal = supratemporal canal (the cephalic lateral line canal (q.v.) running across the top of the head joining the lateral canals. Abbreviated ST).
occipital condyle = the portion of the occipital bone which articulates with the first vertebra (atlas).
occipital crest = a vertical blade on the occipital bone formed from ossification of the connective septum separating occipital myomeres.
occipital joint = the joint between the occiput and the vertebral column.
occipital organ = the organ in male Kneriidae consisting of a cup-shaped opercular organ surrounded by neuromasts and a wedge-shaped, laterally protruding, postopercular organ located behind the gill opening. It serves to hold the male and female together during copulation, apparently functioning as a suction cup.
occipital pit = a cavity in the hind portion of the upper surface of the skull. Apparently of a sensory function. Found in certain Agonidae, e.g. Bothragonus.
occipital region = the posteriormost part of the neurocranium, comprising the exocciptals, basioccipital, occipital, dermosupraoccipital and supraoccipital bones, enclosing a large part of the brain and the membraneous labyrinth and connecting to the vertebral column.
occiput = the back end of the top of the head. Often marked in bony fishes by a line separating scaly and scaleless portions of skin. The adjective is occipital.
occlude = 1) to bring together or close, e.g. jaws.
occlude = 2) to block or prevent passage, e.g. blood in a blood vessel.
occlusal = relating to the biting or grinding of tooth surfaces or the bringing of the opposing surfaces of the teeth of the two jaws into contact.
occlusible = the teeth of the upper and lower jaws fitting together and so allowing mouth closure.
ocean deeps = deep sea areas from 6000 to 10,000 metres.
ocean intercept fishery = a fishery in the ocean directed at stocks of migratory fishes on their way to spawning streams.
ocean perch = a market name for redfish species (Sebastes spp., Scorpaenidae) of the western Atlantic Ocean.
ocean ranching = ranching at sea (commercial raising of fishes. Usually juvenile fish are released to a natural habitat for growth to a harvestable size).
ocean ranging = the release of hatchery-reared juveniles into the sea for growth to marketable size.
ocean run = 1) salmon still in the ocean.
ocean run = 2) a pack of random weight and size fish products.
ocean take = the portion of the total harvest for a species or stock that occurs in marine areas.
ocean type = chinook salmon (Oncorhynchus tshawytscha) populations primarily migrating to the ocean as sub-yearlings, although yearling migrants do occur in some populations. Once in the ocean, they tend to migrate along the coastlines rather than move directly offshore. They have fewer vertebrae (<70) than stream-type chinook salmon (>70). Also called ocean-type fish.
ocean-maturing = steelhead (Oncorhynchus mykiss) that enter fresh water with well-developed gonads and spawn shortly thereafter; commonly referred to as winter steelhead.
ocean-type fish = an anadromous fish that bears no evidence indication on its scales (or other ageing structures) of an extended freshwater residence early in its life. See also river-type fish.
oceanarium = a large seawater aquarium.
oceanaut = an underwater researcher, explorer or swimmer. Also called aquanaut.
oceanic = 1) offshore, the ocean beyond the continental shelf.
oceanic = 2) of, like or near the ocean.
oceanic desert = tropical regions of the ocean (zones of anticyclonic circulations) where zooplankton biomass is low (25-100 mg/m3).
oceanic island = an island in the ocean formed by breaking away from a continental landmass, by volcanic action, by coral formation or by a combination of factors.
oceanic reef = a reef that develops adjacent to deeper waters, often in association with oceanic islands.
oceanic species = species distributed and caught mainly beyond the shelf and/or which migrate extensively across the open ocean. They may have a key stage of their life cycle close inshore and yield large catches in coastal waters. These resources are essentially pelagic for most of their life cycle but some demersal oceanic resources exist on sea-mounts.
oceanic system = waters deeper than 200 m, beyond the shelf break, removed from the effects of surrounding continents and the sea floor.
oceanic zone = the ocean deeper than 200 metres.
oceanodromous = marine fishes which make migrations wholly in the sea, e.g. Clupea, Conger, Thunnus (Myers, 1949).
oceanography = the study of the oceans, its physical features and phenomena. May include biology and ichthyology in some definitions.
oceanology = oceanography (Russia).
ocellate = with ocelli.
ocelli = plural of ocellus.
ocellus (plural ocelli) = an eye-like spot, usually rounded with a lighter border, e.g. the ocellus on the wings of some Rajidae.
ochre = powdered haematite (iron ore) mixed with a liquid to form a rough type of paint. The liquid used included fish oil, among others.
Ockham's razor = Occam's razor.
octacuspid = with 8 cusps or points, e.g. teeth of the characid Cheirodon.
ocular = pertaining to the eye or orbit.
ocular bulb = eyeball.
oculonarial = the region between the eyes and the nostrils; the lateral expansion of the head in Sphyrnidae.
odd fish = an eccentric (slang).
odd-year = fish that spawn in odd-numbered years, e.g. pink salmon, whose distribution is variable although their abundance tends to increase at lower latitudes in both Asia and North America.
odd-year run = a population of fish that returns to its natural spawning grounds in odd numbered years, such as the pink salmon.
odds fish = an oath (archaic).
odons- (prefix) = tooth.
odontes = tooth-like structures, e.g. superficial outgrowths of scales, rays and bones in Denticipitidae.
odontode = the integumentary or skin teeth of conodonts and various fish groups, sometimes lengthened and thickened to form spines. Odontodes have the customary enamel(oid), dentine and pulp cavity structure. However, spongy bone may also be involved and the term may mean slightly different things in different taxa.
odontoid = placoid scale (a type of scale, typically thorn-shaped, found on the skin of Elasmobranchii and claspers of Holocephali. Consists of a spine and a basal plate which is usually rhomboidal. It contains a pulp cavity and is composed of an inner layer of dermal bone, a middle layer of dentine and is covered by enamel-like vitrodentine. Also and less preferably called dermal denticle).
odorant = an odorous substance giving a characteristic smell; fragrant; yielding an odour.
odour = 1) in commercial preparations, the fish species and type of cure has a characteristic odour. Dried heavy-salted and green heavy-salted fish have a salty odour, slack-salted fish have a neutral to cheesy odour and light-salted fish have a neutral to slightly salty odour.
odour = 2) the characteristic smell of fish on the hands can be removed by rubbing them on stainless steel (or carefully on a knife in the field).
Oe = Oannes.
oedema = a swelling; abnormal accumulation of serous fluid in the interfibrillar spaces of connective tissue. Also spelled edema.
oenogarum = garum (q.v.) mixed with wine.
oesophagus = that tubular portion of the gut between the pharynx and the stomach. Also spelled esophagus.
off colour = water conditions such as brown with mud from runoff, green from algal blooms and black from tannic acid.
off flavour = 1) the unacceptable muddy or musty flavour of some fish flesh from pond-raised species such as carp and catfish. The flavour may be caused by blue-green algae in the diet and can be removed by holding the fish in running water for 1-2 weeks. May be hyphenated.
off flavour = 2) spoiled or decaying fish. Associated with oxidative rancidity of lipids, bacterial action, pollutants in the flesh, blue-green algae blooms, etc. May be hyphenated.
off odour = the smell version of off flavour. May be hyphenated.
off-channel habitat = fish habitat not in the main stream channel with water for only part of the year but a refuge for young fishes, e.g. Pacific salmon.
off-channel pool = a pool constructed adjacent to the main flow and connected with it, serving as a protected area for rearing fish.
off-flavour = off flavour.
off-reef = reef slope (the reef seaward of a reef crest).
off-station release = release of fish away from a hatchery, cf. on-station release.
offal = 1) a term used in fish processing for viscera, skin, bones and trimmings which are discarded.
offal = 2) less valuable, coarser fish as opposed to prime or choice fish.
offal = 3) the residue of rendered cod livers.
offer = 1) a strike by a fish at a bait or lure.
offer = 2) Newfoundland slang for offshore, islands, the most seaward of an object, or distant fishing ledges.
Official Correction = a correction, issued by the International Commission on Zoological Nomenclature, of an error or omission in a previously published Opinion, q.v.
Official Index = a list of names or works rejected by rulings of the International Commission on Zoological Nomenclature. The following are compiled and maintained:- Official Index of Rejected and Invalid Family-Group Names in Zoology, Official Index of Rejected and Invalid Generic Names in Zoology, Official Index of Rejected and Invalid Specific Names in Zoology, Official Index of Rejected and Invalid Works in Zoological Nomenclature.
Official List = a list of available names or works which have been ruled on by the International Commission on Zoological Nomenclature. The following are compiled and maintained:- Official List of Family-Group Names in Zoology, Official List of Generic Names in Zoology, Official List of Specific Names in Zoology, Official List of Works Approved as Available for Zoological Nomenclature.
offprint = a separately printed copy of a scientific paper which has also appeared in a journal.
offset hook = a hook offset to the right when viewed from the top of the hook with the eye towards the observer is called kirbed; the opposite offset is reversed. A hook that is not offset is called straight or flat. Kirbed or reversed hooks are all the same to fish but fishermen have strong preferences. Offset hooks are more likely to strike home on fast-biting fish while straight ones work better with slow-biters and chewers. Also flatfish mouth anatomy makes offset hooks more effective. However offset hooks lack the strength of straight ones and can be harder to set in bony or muscular mouths. Offset hooks tend to rotate if trolled or if in a current which may be either an advantage or not.
offset nail knot = a form of nail knot used to connect abruptly tapering lengths of line. See also nail knot and double nail knot. Various websites have animated steps showing how to tie this knot.
offshore = waters away from the shore but under a country's jurisdiction.
offshore barrier = a bar parallel to shore high enough to be above high water. Also called barrier island and offshore beach.
offshore beach = offshore barrier.
offshore current = any current flowing away from shore.
offshore fishery = a fishery taking place beyond coastal waters requiring fairly large vessels.
offshore waters = waters located well beyond the shore, seaward of nearshore or inshore waters.
offstream fish farming = breeding, rearing and farming of fish in offstream fresh, brackish or saline water.
offtake = a channel by which water is removed.
ogival = adjective for ogive.
ogive = 1) a pointed arch, used to describe mouth shape, e.g. in Mugilidae.
ogive = 2) a distribution curve in which the frequencies are cumulative.
ogon = ornamental carp or koi (q.v.), being a single colour metallic fish.
-oid (suffix) = like, e.g. percoid means perch-like.
oikos = habitat.
oil = fish oil is any oil obtained from fishes, usually from the liver, but in fatty fishes from the body, or from fish wastes. Used in fish feeds, edible fats, soaps, paints, leather work and making linoleum.
oil fryer = a metal container filled with hot coals, lowered into a barrel of cod livers, or gurry butt, to assist in the rendering process. The heat helped in the extraction of oil which floated to the surface and could then be scooped off. Modern processes use direct steam injection.
oil globule = a sphere of fat or oil in the yolk of some fish eggs. Variable in number, size, position and colour and so a useful character for identification.
oily fish = fish with a high fat content, having oil or fat around the gut and in the flesh as well as concentrated in the liver. An oily fish fillet may contain up to 30% oil. Oily fish are rich in omega-3-fatty acids and a good source of vitamins A and D, and so are particularly beneficial in human diets compared to white fish, q.v. Often pelagic species.
oil rat = a person who processes cod liver oil, especially transferring it from one container to another (Newfoundland).
old arm = cut-off (2) a lake formed by the closure or cutting off of a bend in a river).
old fourlegs = the coelacanth, Latimeria chalumnae, so called because of its leg-like fin bases.
old river = a river with a low gradient and low erosive energy, characterised by flood plains. See also youthful, mature and rejuvenated rivers.
old salt = 1) salt used in pickling fish that has been stored for three years.
old salt = 2) and elderly or experienced sailor or fisherman.
old style = time reckoned according to the Julian calendar; subsequently replaced by new style (reckoned according to the Gregorian calendar and now in use in the West). Most scientific papers operate on the Gregorian or new style calendar but Russia only adopted the Gregorian system in 1918 and some of their nineteenth century papers and records are asynchronous by 11 days. This can be confusing when attempting to validate type material since catalogues, publications and labels with the types in jars can have different dates. Abbreviated as OS. See also new style.
older synonym = an earlier synonym that cannot be used as the name for the taxon under the provisions of the International Code of Zoological Nomenclature.
old tank syndrome = accumulation of organic acids, excess nitrates, and other products in an aquarium, causing a gradual decline in pH or a sudden pH crash. Can be avoided by regular partial water changes. See new tank syndrome.
old trout = 1) nothing to do with trout, a disparaging term for an unattractive, older and sometimes rich, woman, or an unpleasant, and troublesome older woman. See also trout.
old trout = 2) a familiar form of address to a male friend, often as "my old trout", "me old trout".
old water = water with organic waste that restricts growth, cf. new water.
olfaction = the sense of smell; chemoreception by nasal organs.
olfactory = pertaining to the nasal organs or the sense of smell.
olfactory bulb = a large organ of smell, e.g. in sharks. This is the most anterior part of the brain but is distinct from the telencephalon while anteriorly it merges with the olfactory nerve.
olfactory cavity = the space occupied by the olfactory rosette.
olfactory lamella = one of a series of lamellae lined by olfactory epithelia and forming the olfactory rosette. Absent in some fishes such as Belone belone, Gambusia agiffi, Poecilia reticulata, Ammodytes lancea and Syphonostoma typhle.
olfactory nerve = cranial nerve I, conducting odour stimuli from the olfactory organ to the brain.
olfactory organ = the organ of smell.
olfactory pit = a shallow depression on the snout of larval fish from which the olfactory organ develops.
olfactory rosette = nasal rosette (the lamellae and associated elements of the nostril). May be radial, arrow-shaped, parallel or bilateral.
olfactory ventilation sac = an extension of the olfactory cavity, often characteristic of inactive bottom dwellers living in still water such as flatfishes, dipnoans, and eels but also found in clupeids, salmonids, mugilids and scombrids. Primarily used for ventilation but also produce mucus. There may be up to four sacs, usually the additional sacs are smaller but in Osmeridae the sole accessory sac is larger than the main sac. Also called accessory olfactory sac.
Oligocene = a geological epoch within the Tertiary Period ca. 38-26 million years ago.
oligo- (prefix) = few, several, somewhat, little.
oligohaline = 1) organisms tolerant of only a moderate range of salinities.
oligohaline = 2) brackish water with a salinity of 0.5 to 3.0 (or 5.0) parts per thousand from ocean-derived salts.
oligohaline = 3) sea water having a salinity of 17 to 30 parts per thousand.
oligomictic = a lake having relatively stable stratification with only rare periods of circulation.
oligophagous = restricted diet, eating few food types.
oligosaline = 1) organisms able to live in brackish water.
oligosaline = 2) brackish water, water of intermediate salinity, 0.5-5.0 p.p.t. from land-derived salts.
oligothermic = tolerating or confined to relatively low temperatures.
oligotrophic = 1) adjective for oligotrophy.
oligotrophic = 2) an organism requiring only a small nutrient supply or a narrow range of nutrients.
oligotrophy = a lake condition with low productivity, hence the hypolimnion does not become depleted of oxygen. Usually having a deep, narrow basin and clear waters with little littoral vegetation.
oligotypic = a taxon with few members.
olim = formerly.
olivette = very small cylindrical, tear-drop or elongate diamond-shaped lead weights used on float rigs in angling. They are placed on the line beneath the float to ensure stability in fast, deep water. Held in place by shot or plastic pegs.
olympic-style fishing = a race-to-fish management system where individual boats race to take as much of the total allowable catch before the fishery closes.
omega eye = omega iris.
omega iris = a special iris structure found in armoured suckermouth catfishes (Loricariidae). The top part of the iris descends in a loop similar in shape to the Greek letter omega (Ω) in an upside down position. The loop can expand when light levels are high to cover the pupil centre forming a c-shaped light transmitting portion. It may also serve to break up the distinctive eye outline in a fish that is heavily camouflaged.
omega-3-fatty acid = long-chain polyunsaturated fatty acids (PUFAs) found in fishes. They have a beneficial effect on the human cardio-vascular system and reduce risks of cancer, diabetes, arthritis and autoimmune diseases. Docosahexaenoic acid, q.v., and eicosapentaenoic acid, q.v., are the principle acids.
omni- (prefix) = all, universally.
omnivore = feeder on both plants and animals.
omnivorous = eating both plants and animals.
omopterygia = plural of omopterygium.
omopterygium (plural omopterygia) = pectoral fin (the paired fin born by the pectoral girdle, usually just behind the gill opening or slightly dorsal or ventral to this position. Also called homopterygium. This fin is generally larger than the pelvic fin and less variable in position and structure. The pectoral is low on the body in more primitive bony fishes and higher in more advanced ones. It functions to steer, brake and propel the fish. Pectoral fin ray counts include all the rays branched and unbranched. The length is measured from the origin (upper or outer part of base) to the distal tip of the fin. Abbreviated as P or P1).
on the flake = spending the summer laying out cod to dry on the flakes (q.v.) (Newfoundland).
on your own hook = on your own, on your own responsibility. Derived from nineteenth century fishermen on the Grand Banks who were paid by what they caught on their own hooks and line.
on-demand feeder = aquaculture feeding systems where timing and quantity of food is determined by the fish, e.g. by pressing a lever.
on-station release = release of fish at a hatchery, cf. off-station release.
on-the-drop = angling with a float rig that sinks slowly in the water for catching fish high in the water column.
on-the-feed = fish feeding or looking for food.
onboard observer = a government official on board a vessel monitoring fishing and processing and collecting harvest data.
One Fish Two Fish Red Fish Blue Fish = a 1960 rhyming book for children by Dr. Seuss.
one-claw jigger = type of fishing-hook with a single barb, used without bait.
one-sea-winter salmon = a salmon, Salmo salar, which has spent one winter at sea (usually given as 1-sea-winter salmon); equivalent to a grilse, q.v., when maturing to spawn. There are also 2-sea-winter salmon, 3-sea-winter salmon, etc.
one-tub set = a single tub of line set out in trawl fishing.
ongrowing = raising fish to marketable size in aquaculture.
onomatography = the correct writing of animal and plant names.
onomatophore = a specimen acting as the name bearer; a nomenclatural type; type; nomenifer.
onomatype = a specimen which has been previously cited in print but which has not been used to illustrate anything not previously known about the morphology of the species or subspecies.
onshore = a direction landward from the sea, e.g. onshore wind, onshore current.
onshore waters = shallow waters at a small distance from the shore. Also called inshore or nearshore waters.
ontogenesis = the process of development from embryo to adult.
ontogenetic = adjective for ontogeny.
ontogeny = the development from embryo to adult.
oo- (prefix) = egg.
oocyte = oogonia become oocytes when meiosis begins and specialised cells surround each oocyte to form a follicle. The oocyte undergoes a maturation in preparation for spawning as an egg. The nucleus enlarges and its membrane becomes irregular, the cytoplasm becomes vacuolated, yolk is deposited and a zona radiata develops around the oocyte.
oodiniasis = infection with a dinoflagellate protozoan of the genus Oodinium, e.g. coral fish disease, q.v.
oogenesis = the formation and development of eggs.
oogonia = plural of oogonium.
oogonium (plural oogonia) = oogonia resemble undifferentiated germ cells in embryos. They undergo mitosis and proliferation to form oocytes; the process involves increase in cell and nucleus size.
oom = a slight sensation detected by a fisherman holding a line, indicating fish nibbling at the bait (Scottish dialect).
oophagy = 1) eating eggs.
oophagy = 2) a specialised mechanism for nourishing embryos where the embryos, while in the uterus or oviduct, feed on maternal eggs, e.g. in Alopias pelagicus (Alopiidae).
oothy = a smooth surface made on the sea by throwing out crushed limpets or mussels as inshore bait for coalfish (Pollachius, Gadidae) (Orkney dialect). Also spelled uthy.
ooze = a muddy deposit of the deep ocean composed mostly of shells, foraminiferans and diatoms, or mud saturated with water.
oozing = fully ripe fish gonads where milt or eggs are leaking from the vent.
OP = 1) photophores just posterior to the end of the upper jaw in Myctophidae.
OP = 2) photophores on the gill cover, one near the anterior base of the preopercle, one in front of the anterior part of the subopercle, and one antero-dorsally to the operculum.
OP = 3) abbreviation for opercular canal.
op. cit. = abbreviation for opera citato.
opaque zone = a dark zone in an otolith that, relative to other zones, restricts the passage of light. Under reflected light this zone appears bright.
open access equilibrium = when all of the excess profits or economic rent that attracts new entrants to a developing fishery have been dissipated in the costs associated with the additional fishing effort. The fishery is no longer attractive to new entrants. Usually occurs when fishing effort is higher than that which will obtain the greatest yield from a fishery.
open access fishery = fishery where there is no limit on the number of fishers. Usually refers to recreational fisheries. Frequently over-exploited and degraded.
open brooder = the condition in some Cichlidae that lay eggs on an open surface, such as rocks, sand, and plants. The eggs are usually numerous, small and clump together. Clear sexual dimorphism and dichromatism is usually evident, e.g. Pterophyllum, Symphysodon, and most species of Cichlasoma.
open face spinning reel = a reel where the line is allowed to peel off the spool when a bale arm is turned aside. There is little or no friction as the reel does not turn as the line comes off.
open ice = ice covering five-tenths to eight-tenths of the water surface. Also called broken ice, loose ice, loose pack ice, open pack ice, slack ice.
open lake = a lake which has an outlet.
open pack ice = open ice.
open sea = the open part of a sea or ocean, extending outward from the continental shelf, usually outside territorial waters.
open season = the time period when angling is allowed for any given species, cf. closed season.
open substrate spawner = fish that broadcast large numbers of eggs and do not guard them.
open water = 1) freely navigable water where sea ice is less than 10%.
open water = 2) water away from land including the upper water layer of a lake.
open-end swimfeeder = a plastic swimfeeder (q.v.) without ends and often with holes in the sides allowing quick release of groundbait (q.v.).
open-mouthed skiff = a type of large, undecked fishing-boat.
opening = the scheduled beginning of a fishery that may last hours to months.
opera citato = in the publication (but not page) cited; used to avoid repetition of a reference in full.
operational sex ratio = the ratio of males and females available to mate with one another. Not the same as the sex ratio.
operational unit = a group of vessels fishing in the same way for the same species.
opercle = the principle and largest, paired dermal bone comprising the upper part of the gill cover above the subopercle. Sometimes used in aging studies.
opercula = plural of operculum.
opercular = pertaining to the operculum; often used for the opercle.
opercular canal = the cephalic lateral line canal (q.v.) on the opercle.
opercular flap = a postero-dorsal fleshy part of the gill cover, either composed solely of skin or also supported by an extension of the opercle. See also opercular lobe.
opercular head spine = a spine on the head of Scorpaenidae members. They are, from anterior to posterior over the top of the head on each side, the nasal, preocular, supraocular, postocular, tympanic, coronal (medial to the tympanic and postocular spines), parietal, and nuchal. Opercular spines are at the postero-dorsal corner of the operculum, preopercular spines line the posterior margin of the preoperculum, and the cleithral and postcleithral spines are just above the opercular spines on the side of the head.
opercular lobe = a postero-dorsal fleshy part of the gill cover, either composed solely of skin or also supported by an extension of the opercle. See also opercular flap.
opercular membrane = the tissue covering the gills laterally and enclosing (including in some, but not other definitions) the opercle, preopercle, subopercle and interopercle bones. In most Teleostei, where the membranes from each side meet under the head on the isthmus, the left side overlaps the right.
opercular opening = gill opening.
opercular photophore = one of a series of light organs located on the gill cover behind the end of the jaw in Myctophidae. Abbreviated OP.
opercular pumping = sucking or blowing water through the mouth by means of lifting the operculum to create a suction mechanism. Used by some fishes to aerate their eggs.
operculum (plural opercula) = the flap externally closing the gill chamber and usually supported in Teleostomi by the opercle, propercle, subopercle and interopercle; the gill cover. In some definitions, synonymous with the opercular membrane.
opere citato = in the publication (but not page) cited; used to avoid repetition of a reference in full.
ophioblennius stage = a pelagic stage of some salariin Blenniidae characterised by enlarged pectoral fins, and enlarged, hooked teeth anteriorly in the lower jaw or in both jaws.
Opinion = a decision of the International Commission on Zoological Nomenclature applying, interpreting or suspending the provisions of the Code and stating what actions are to be taken, published in the Bulletin of Zoological Nomenclature.
opistho- (prefix) = behind, reversed or opposite.
opisthocœlian = opsithocoelous.
opisthocoelous = vertebral centra which are concave posteriorly and convex anteriorly. e.g. in Lepisosteidae.
opisthonephros = mesonephros (the functional organ of excretion in all adult fishes except Myxini. Arises in the middle portion of the body cavity but extends backwards to the entire length of body cavity. Has a large number of tubules).
opisthotic = a deep, endochondral bone forming the ventral element of the otic capsule, covering the ampulla of the posterior semicircular canal. Sometimes applied to the autopterotic. Present in fossil Crossopterygii and Actinopterygii, lost in Amia, Lepisosteus and modern Teleostei and therefore the name intercalar is more accurate for these fishes.
opisthure = 1) the tip of the vertebral column which protrudes beyond the caudal fin, e.g. in larval Elasmobranchii.
opisthure = 2) urostyle (1) the small upturned posterior tip of the vertebral column, generally formed of a slender, pointed rod of cartilage, or fused vertebrae and associated elements (in homocercal caudal fins of Teleostomi) and (2) the fan-like series of bones articulating with the last true vertebra, including preural centra, ural centra, epurals and hypurals. Counted as one vertebra in some vertebral counts, not counted in others.
opportunistic = taking advantage of unused or little used resources.
opportunistic feeding = feeding in which the fish is able to adapt to whatever food becomes available.
opportunistic fishing = where the fishing unit targets species and fishes in areas where fishing opportunities are greatest.
optic = 1) adjective regarding the eyes.
optic = 2) a type of artificial fly with an enlarged head and obvious eyes.
optic cup = a stage in eye development with an inner layer developing as the neural retina and an outer layer forming the pigmented retina.
optic lobe = one of the paired structures of the brain, q.v. forming the mesencephalon.
optic muscles = the arrangement of muscles that move the eye is variable in fishes. In Perca flavescens, for example, the muscles comprise the inferior, superior, lateral and medial recti muscles and the superior and inferior oblique muscles.
optic nerve = each optic nerve emerges from the anterior ventral corner of each optic lobe. The nerves cross over beneath the telencephalon.
optic pedicel = a cartilaginous rod projecting from the skull and supporting the eyeball in Elasmobranchii and Teleostei
optic primordium = the lateral outgrowth from the forebrain that becomes the eyeball, excluding the lens. It develops into the optic cup.
optic tectum = the dorsal roof of the mesencephalon concerned with vision.
optic ventricle = a cavity in the brain, one in each optic lobe.
optimum age = the average age of the fish in a year-class at which the instantaneous rate of natural mortality equals the instantaneous rate of growth in weight for the year-class as a whole. At this age, the biomass of the age class is maximum.
optimum fishing capacity = the balance between inputs and outputs, e.g. minimising costs while producing a sustainable harvest. Current or transient optimal capacity (related to current fleet and stock conditions) may differ from long run optimal capacity (reflecting management long-term objectives) particularly if the fishery resource is currently depleted and the management strategy is to rebuild this depleted resource.
optimum size = critical size (the average size of the fish in a year-class at the time when the instantaneous rate of natural mortality equals the instantaneous rate of growth in weight for the year-class as a whole). At this size, the biomass of the age class is maximum.
optimum sustainable yield = optimum yield.
optimum take = the annual catch from a stock which is economically viable, does not alter the ecosystem significantly and does not affect the reproductive potential of the stock.
optimum yield = the yield from a fishery which provides the greatest overall benefit to the nation with particular reference to food production, recreational opportunities and conservation or, allows rebuilding of overfished stocks. It is based on maximum sustainable yield (q.v.) as modified by economic, social or ecological factors. Generally catches are kept at less than the maximum sustainable yield as this keeps the biomass on the high side (and also it is not easy to assess what the maximum sustainable yield is). At this lower level there are more fish that are bigger, easier to catch and less expensive to do so, of better value, and easier to process. Note that the optimum may not be more big fish. It may be a longer season or many small fish as with sardines. The downside is fewer fishery jobs.
oral = pertaining to the mouth.
oral brooder = a fish which broods or protects the eggs (ovophile) or young (larvophile) by taking them into the mouth.
oral cavity = the shallow vestibule anterior to the pharynx, between the first row of gill rakers and the mouth.
oral disk = the circular mouth area of lampreys (Petromyzontidae) bearing horny teeth.
oral fimbria = one of a series of small tag-like appendages around the perimeter of the oral disc of lampreys (Petromyzontiformes), presumed to help create an effective seal when the lamprey is attached to its host and also probably sensory. Also called fringed processes, leaf-like processes, epithelial fringe, fringed lappets, leathery appendices and leathery appendages.
oral gestation = oral incubation.
oral grasping = a behaviour observed in members of the family Cyprinidae in laboratory flumes where the fish use the mouth to hold onto mesh screens as a station-holding method. Monocanthidae orally attach to sponges, tunicates, rope and fishing line in nature as a nocturnal mooring behaviour.
oral hood = a scoop-like structure formed by prolongation of the lips around the vestibule which leads to the mouth in Amphioxi and larval Petromyzontiformes.
oral jaw = the typical jaw of the mouth region as opposed to the internal jaw or pharyngeal teeth and associated structures.
oral incubation = mouth-breeding or the care and hatching of fertilized eggs in the mouth. Also called buccal incubation and, less aptly, oral gestation, e.g. certain Apogonidae, Ariidae, Anabantidae, Osteoglossidae.
oral papilla = one of a series of short, finger-like extensions of the skin immediately outside the oral fimbriae, q.v., possibly of a sensory function.
oral plate = a band of tough connective tissue bearing teeth anterior and posterior to the oral opening in Petromyzontidae.
oral valve = the flap attached just inside the jaws which stop water escaping from the mouth during exhalation, helping to maintain a unidirectional flow. Usually a valve is found just inside the ring of teeth in the jaw. Also called a buccal valve.
orange meat = a discolouration of the flesh of skipjack tuna occurring sometimes when brine-frozen and affecting marketability.
ORB = photophores near the eye; one antero-ventral to the eye is called the suborbital (or preorbital) and one postero-ventrally is called the postorbital.
orbicular = round, circular, nearly circular.
orbicular stadia or stage = a larval stage in some Acanthuridae where the body is almost spherical, translucent and covered with vertically elongated ridge-like serrated peduncular scales in distinct vertical rows. The first dorsal spine is the longest and stoutest spine and the rays become progressively shorter behind this.
orbit = the cavity in the skull enclosing the eye, the eye socket.
orbital = pertaining to the orbit.
orbital bones = the bones around the eye.
orbital diameter = either the greatest or the horizontal distance between the rims of the eye socket. Best measured as the greatest distance between the bony rims, or between the fleshy rims.
orbital fenestra = a centrally located opening in the head shield of some Placoderms for the eyes and nostrils.
orbital horn = a bony projection near the eye.
orbital region = the head around the eye comprising such dermal bones as the antorbital and infraorbitals (bearing a sensory canal) and the suborbitals and supraorbitals (without a canal).
orbitosphenoid = a deep, median or paired, endochondral bone underlying the frontal bone forming the floor and walls of the anterior end of the cranium. Visible in the wall of the orbit. Absent in Salmonidae and Gadidae, for example.
orbitostylic = a type of jaw suspension in which the upper jaw is attached to the braincase near the orbits, generally by a strong, but somewhat flexible soft tissue connection, e.g. in Squalus acanthias.
order = a taxonomic category above the family-group and below the class-group. The ordinal-group includes in ascending sequence the suborder, order and superorder. The International Code on Zoological Nomenclature does not consider the ordinal-group. In the Berg system, which uses the ending -iformes, the ordinal name is based on the family name of a well known family in the order.
ordinary cure = cod salted and dried in a manner intermediate between light and heavy salted grades.
ordinary high water mark = the usual and most common high water level found on a bank or bed. Above this point the soil has a distinct character and vegetation.
ordinary tide = not a technical term but equivalent to mean.
Ordivician = a geological period within the Palaeozoic ca. 504-441 million years ago. Abbreviated as O.
Oregon moist pellet = moist pellet (a pellet used in aquaculture with a moisture content around 30%. Composed of wet ingredients such items as minced fish, and dry ingredients such as fish meal, cereals, vitamins and minerals, with an alginate binder).
oreosoma = the distinctive young of the family Oreosomatidae characterised by scutes or horny protuberances in a leathery skin and thus unlike the adult.
organic bait = any organism or food used as bait in angling, e.g. worms, insects, fish eggs, minnows, cheese, bread, etc.
organism = any living entity.
organ, contact = contact organ (the dermal bony outgrowth or spicule projecting from a fin ray or scale margin and surrounded by the epidermis through which bony outgrowths may protrude. Present in those parts of the body and fins of the male which come in direct contact with the female during the spawning act. May be tactile in function. Found in 9 families of 3 orders: Cypriniformes, Atheriniformes, and Scorpaeniformes (Wiley and Collette, 1970)).
organ, pearl = breeding tubercle (usually small, raised, epidermal structures on regions of the head, body, or fin rays where two individuals come in contact. May consist of aggregations of non-keratinized epidermal cells, the same with a light, superficial keratinized cuticle, or with substantial number of fully keratinized cells that are organized to form a discrete, usually conical cap. Breeding tubercles may function to maintain body contact between the sexes during spawning; in the defence of nests and territories; in the stimulation of females in courtship; and in some forms perhaps in sex and species recognition. Also called nuptial tubercles. Found in 15 families of 4 orders; Salmoniformes, Gonorhynchiformes, Cypriniformes, and Perciformes (Wiley and Collette, 1970)).
organ of Fahrenholz = organs consisting of blind tubes that extend deep into the body in Dipneusti and Polypteriformes. In Polypteridae they are found only on the head and most commonly above the mouth. In the Dipneusti they are found over the whole body except the fins. The crypts are surrounded by a plexus of nerve fibres and are probably sensitive to electric stimuli.
organ of Pinkus = one of several diverticula in the spiracle of Mustelus and Squalus, or a dorsad running channel from the spiracle with three sensory organs at the end, or closed vesicles each with a sensory organ in Protopterus and Lepidosiren. The receptors can be considered as neuromasts but show similarities to the ampullae of Lorenzini. Their function is unknown.
organ of Sachs = the electric organ in the posterior part of the body in Electrophorus.
organic bait = any live or food bait, e.g. minnows, worms, cut bait, cheese, etc.
organic manure = manures added to fish ponds which, through decomposition by microorganisms, provides nutrients for plant growth. Farmyard faeces, urine, night soil, green manure, compost and silkworm dregs are all used.
organogenesis = a late stage of embryonic development where organ systems are formed.
organoleptic = pertaining to a sensory organ, usually taste, but can be smell. Often found in accounts of taste tests of fish preparations such as marinades.
organoleptic analysis = detecting off fish by smell.
oriental = eastern or easterly.
oriental cure = salted ungutted herring prepared in North America for trade to the Far East.
origin (fin) = the anterior end of the base of a fin. Opposite of insertion.
origin (muscle) = the relatively fixed attachment of a muscle. Opposite of insertion.
original date = the date of publication of an available work containing a nomenclatural act, a name or a nominal taxon.
original description = the description of a taxon when first established.
original designation = the designation of the type of a taxon when first established.
original diagnosis = a formal statement of characters which distinguish a taxon from other similar or closely related taxa, published at the time of proposal of a new taxonomic name.
original fixation = the fixation of the type by original designation or by monotypy.
original material = all material used by an author in the preparation of the original description of a taxon. Includes specimens, illustrations and descriptions.
original publication = the work in which a name or nomenclatural act was first published.
original spelling = the spelling of an available name when first published. The original spelling of a name is to be kept as the 'correct original spelling' unless it does not meet the requirements of the International Code of Zoological Nomenclature. An incorrect original spelling is an original spelling that is incorrect. Multiple original spellings are two or more different original spellings for the same name.
ornamental species = fish bred and reared in captivity for the aquarium trade.
ornamentation = frills, flaps, tags and other extensions of fins and the body of a fish used in concealing the body from predators or in reproductive behaviour.
orobranchial chamber = both the mouth and gill cavities. Sometimes defined as the gill cavity immediately adjacent to the mouth cavity. See also parabranchial chamber.
oronasal curtain = the internasal flap, a fleshy flap between the nostrils; in Chondrichthyes may cover part of the mouth.
oronasal groove = a groove leading from each nostril to the corresponding corner of the mouth in many Elasmobranchii.
oropharynx = the section of the alimentary canal comprised of the oral and pharyngeal cavities.
orphan collection = a scientific collection of fishes that has lost financial and curatorial support or that has been abandoned by the owner.
orphan virus = an orthomyxovirus-like agent isolated from bluegills (Lepomis macrochirus).
orphaned = said of an orphan collection.
orth. mut. = abbreviation for orthographia mutata.
ortho- (prefix) = straight, upright, at right angles.
orthodont = a type of tooth vascularisation in Chondrichthyes by means of an internal pulp cavity radiating into numerous tiny canals penetrating the orthodentine layer (Herman et al., 1994), cf. osteodont.
orthographia mutata = with an altered spelling.
orthographic error = an unintentional misspelling.
orthographic variants = 1) two or more different spellings of the same name.
orthographic variants = 2) names of two or more taxa with spellings so similar that they may be confused.
orthography = spelling or usage of words.
orthotype = a type by original designation.
ory = fish with a smell or taste of seaweed (English dialect).
OS = old style.
os (plural ossa) = bone (the hard connective tissue consisting of cells (osteoblasts, osteocytes) in a mixture of collagen fibres and hardened by calcium and phosphate salts (calcium hydroxyapatite), serving to support the body. The cells are lost eventually leaving cavities and the bone is termed cellular, typical of Dipnoi, Crossopterygii, Chondrostei, primitive Teleostei, e.g. Cyprinidae, Siluridae, Salmonidae, Anguillidae, and some advanced Teleostei, e.g. Perca, Gadus. Another form of bone is termed osteoid and lacks the ramifications seen in cellular bone. After the osteocytes disintegrate, the spaces they leave are filled with matrix and the bone is known as acellular, e.g. in Cyclopterus, Mola. Bone is strong and rigid in contrast to cartilage). Older works on fish anatomy may have bones listed in Latin, hence the following entries. Plural forms are given for those unfamiliar with Latin. Note that some bone and skeletal names in English are the same in English and Latin, e.g. branchiocranium, and the majority of English names are derived from the Latin name, merely having different word endings.
os actinostum (plural ossa actinosta) = actinost (one of a series of endochondral bones in the pectoral and pelvic girdle on which the fin rays insert. Most teleosts lack or have greatly reduced pelvic actinosts. Teleosts have one row of actinosts between the fin rays and supporting skeleton (coracoid and scapula for the pectoral, basipterygia for the pelvic) while other fishes may have more rows, referred to as radials).
os adnasale (plural ossa adnasalia) = adnasal (a small dermal bone in front of the nasal bone in some fishes, e.g. the middle bone of three in the nasal region of Lepisosteus).
os alisphenoidale (plural ossa alisphenoidalia) = alisphenoid (term misapplied in older literature to the pterosphenoid (q.v.) of fishes. It is not homologous with the alisphenoid of mammals and should not be used).
os angulare (plural ossa angularia) = angular (the triangular, paired dermal bone on the posterior ventral corner of the lower jaw. Also applied to the dermal bone of the lower jaw which articulates posteriorly with the quadrate, in which case the preceding bone is known as the retroarticular. In mammals this bone becomes the malleus of the inner ear).
os antorbitale (plural ossa antorbitalia) = antorbital (a small, paired dermal bone lying lateral to the nasal bone in front of the eye. Sometimes included in the suborbital or infraorbital series because the infraorbital canal crosses it, e.g. in Amiidae, Lepisosteidae, Elops, Osmeridae, some Siluridae).
os articulare (plural ossa articularia) = articular (the deep, endochondral bone of primitive acanthopterygians in the middle of the lower jaw between the dentary and the angular (or retroarticular) which articulates with the quadrate. It is later invaded by the angular. Divided into the distal part (wanting in Teleostomi) and the proximal part. Occupies the position of Bridge's ossicles b and c in Amia. Found as a distinct structure in Amia, Lepisosteus, Polyodon and Acipenseridae).
os auditorium (plural ossa auditoria) = one of the Weberian ossicles (the four bones in a chain derived from vertebrae in the Weberian apparatus forming the auditory unit or pars auditum (anterior to posterior): claustrum, scaphium, intercalarium and tripus).
os autopalatinum (plural ossa autopalatina) = autopalatine (a paired deep bone on the roof of the mouth, lateral to the prevomer (or vomer). Often called palatines. Usually overlain by the dermal, often tooth-bearing bone, the dermopalatine).
os autopteroticum (plural ossa autopterotica) = autopterotic or pterotic (the paired deep bone and the superficial dermal bone covering it forming the lateral roof of the skull between the parietal and the hyomandibular and in contact with the lateral semicircular canal).
os autosphenoticum (plural ossa autosphenotica) = autosphenotic (the deep bone comprising the postorbital process. Often called the sphenotic, it is overlain by the dermosphenotic or postorbital).
os basibranchiale (plural ossa basibranchialia) = basibranchial (one of the deep median bones at the base of the gill arches below the hypobranchials. May occur on arches 1, 2, 3, 4, the last being cartilaginous. The dermal plates bearing teeth and associated with the basibranchials are a separate structure. Each of the basibranchials may be called a copula and the first is named the basihyal).
os basihyale (plural ossa basihyalia) = basihyal (the cartilage supporting the tongue at the anterior end of the hyal series in Elasmobranchii. It is the anteriormost median endochondral bone of the basibranchial series, joining both branches of the hyoid series and forming the tongue skeleton in Teleostei. Dorsally is may have a dermal tooth plate called the glossohyal. The basihyal does not always ossify, e.g. in Salmonidae).
os basioccipitale (plural ossa basioccipitalia) = basioccipital (the deep, median, endochondral bone at the posterior end of the parasphenoid on the ventral side of the posterior end of the skull. The bone with which the anterior-most vertebra articulates, it also forms the ventral part of the foramen magnum. In Cyprinidae it bears a posterior expansion forming the pharyngeal process).
os basipterygium (plural ossa basipterygia) = basipterygium (plural basipterygia)(one of the endochondral fused radials or pterygiophores at the base of a fin, particularly the pelvics. The two chondral basipterygia of the pelvic fin meet anteriorly at the pubic symphysis to form the pelvic girdle. The body of the bone is called the pubic plate and bears an acetabular facet for articulation of the fin rays or the radial bones. An anterior process is known as the pubic process, a middle as the iliac process and a posterior as the ischial process. Also called basalia or pelvic bone. It articulates with the antimere, q.v., the corresponding bone on the opposite side).
os basisphenoideum (plural ossa basipsphenoidea) = basisphenoid (the small, Y-shaped, deep, endochondral cranial bone ventrally covered by the parasphenoid and medial to the pterosphenoids forming part of the floor of the neurocranium and the base of the posterior myodome. The bone ossifies from the medial belophragm and two lateral meningosts that form the wings. It is cartilaginous in Ostariophysi and lost in, e.g., Gadidae).
os branchioperculum (plural ossa branchiopercula) = branchiopercle (a fourth bone of the opercular series in Amia, partially covered by the subopercle and interopercle, but regarded as the most dorsal branchiostegal ray by authors).
os branchiostegale (plural ossa branchiostegalia) = branchiostegal (one of the dermal bony (or cartilaginous) struts inserting on the epihyal and/or ceratohyal and sometimes the interhyal and hypohyal, and supporting the branchiostegal membranes. Of various forms from narrow, to plate-like to hooked, with numbers varying according to phylogeny, up to 50 in Actinopterygii to none in Crossopterygii. Less preferably called branchiostegal rays because of confusion with the fin rays).
os circumorbitale (plural ossa circumorbitalia) = circumorbital (one of a series of superficial dermal bones encircling the eye including the suborbitals and supraorbitals. A complete circuit of bones is found only in such primitive fishes such as Lepisosteus and some Osteoglossidae).
os cleithrum (plural ossa cleithra) = cleithrum (plural cleithra)(the principal bow-shaped bone of the pectoral girdle, dermal in origin, forming the rear margin of the gill cavity. It articulates dorsally with the supracleithrum and ventrally with the scapula and coracoid, and meets its opposite pair medially under the heart. Used in age estimation, where it is more reliable than scales in some species, e.g. Esox masquinongy).
os coracoideum (plural ossa coracoidea) = coracoid (the lower, paired endochondral bone on which the pterygials or actinosts of the pectoral fin rest. Dorsally it has a notch which, with a similar ventral notch on the scapular, frames the scapular foramen. It attaches anteriorly to the cleithrum).
os coronomeckelium (plural ossa coronomeckelia) = coronomeckelian (a small bone on the postero-lateral part of Meckel's cartilage of the lower jaw. Often a point of insertion of the adductor mandibulae muscle. Also called sesamoid angular, supraangular, sesamoid articular, articular sesamoid, splenial, os meckeli or d bone).
os coxa (plural ossa coxae) = innominate bone (the pelvic fin bone in Gasterosteidae, sometimes a misnomer for the ectocoracoid. Also called pelvic bone, pelvic plate, posterior process, pubic bone and medial plate).
os dentale (plural ossa dentalia) = dentary (the anterior, paired, dermal bone in the lower jaw. Usually the only tooth-bearing bone in the mandible, the two halves have a V-shape and meet at the jaw tip or mandibular symphysis. Posteriorly it has a coronoid process directed dorsally and a ventral process bearing the mandibular sensory canal on its outer face).
os dermoarticulare (plural ossa dermoarticularia) = dermarticular (the dermal bone of the lower jaw laterally covering and often fusing with the angular or retroarticular).
os dermopalatinum (plural ossa dermopalatina) = dermopalatine (the paired dermal bone covering the undersurface of the autopalatines (q.v.) which are commonly called palatines, especially when the dermopalatine and autopalatine fuse).
os dermosphenoticum (plural ossa dermosphenotica) = dermosphenotic (a superficial dermal bone behind the eye comprising the sixth infraorbital or suborbital; the dermal representative of the autosphenotic. Bears part of the suborbital and sometimes the conjunction of temporal, and supra- and suborbital sensory canals).
os dermosupraoccipitale (plural ossa dermosupraoccipitalia) = dermosupraoccipital (the superficial, paired dermal bone covering the supraoccipital with which it may fuse. In many Teleostei it is a hinge for the skull articulation with the circumorbital ring. Siluridae have a posterior toothed process that secures the nuchal disc. Also called parietooccipital, postparietal or dermal supraoccipital).
os ectocoracoideum (plural ossa ectocoracoidea) = ectocoracoid (a paired dermal bone in Gasterosteiformes connected with the coracoid and extending posteriorly. Has also been applied to the element below the scapula and applied to the coracoid in Dipnoi).
os ectopterygoideum (plural ossa ectopterygoidea) = ectopterygoid (a paired, deep, dermal bone forming part of the roof of the mouth, articulating anteriorly with the palatine, posteriorly with the quadrate and mesially with the endoptetygoid if the latter is present. In Amia it has one or two rows of teeth. Sometimes called pterygoid when there is no endopterygoid).
os epihyale (plural ossa epihyalia) = epihyal (the deep, endochondral bone at the upper end of the hyoid arch below the interhyal. It joins the hyomandibular and the symplectic through the interhyal, and articulates with the ceratohyal by a suture in some fishes, e.g. Gadidae. May bear a dentigerous plate. Also called dorsal ceratohyal or posterohyal as it is considered to be the dorsal ossification of the ceratohyal. May or may not be homologous with the epal element of the branchial arches).
os epioocciptale (plural ossa epioccipitalia) = os epioticum.
os epioticum (plural ossa epiotica) = epiotic (the deep bone and the superficial bone overlying it which form the upper element of the otic capsule, and lie posterior to the parietal, ventral to the supraoccipital, and dorsal to the pterotic. It covers the posterior semicircular canal. It is considered to be an ossification of the occipital arch that has invaded the otic region and so is often called epioccipital).
os epurale (plural ossa epuralia) = epural (an elongate detached bone above the urostyle and behind the last neural spine supporting caudal fin rays. Apparently derived from neural spines or the urostylic centra; dorsal homologues of the hypurals. Vary in number between one in advanced fishes to three in primitive actinopterygians).
os ethmoidale (plural ossa ethmoidalia) = ethmoid (the deep, embryonic, perichondral, cartilaginous bone ossifying in and around the nasal septum. Later covered by the nasals, prevomer, adnasals (and rostrals) and located anterior to the orbit. It may not ossify in some Teleostei. Also called hypethmoid and dermethmoid).
os ethmoideum laterale (plural ossa ethmoidea lateralia) = parethmoid (a paired deep bone of perichondral origin lying in the front of the orbit under the prefrontal. Also called pleurethmoid, prefrontal, exethmoid and, incorrectly ectethmoid, as this latter is only in birds).
os frontale (plural ossa frontalia) = frontal (the superficial, paired dermal bone on top of the skull above the eyes, paired or fused into one. The frontals of fishes correspond to the parietals of Tetrapoda but frontal is retained on account of its long usage in fish osteology. These large bones cover much of the neurocranium and may fuse with the lateral ethmoids and articulate with some of the circumorbital bones, the spehenotic and the pterotic. In the parietolateral skull type, the parietals are separated allowing the frontals to meet the supraocciptal).
os glossohyale (plural ossa glossohyalia) = glossohyal (the median dermal toothed bone at the anterior of the hyoid series. It covers dorsally the cartilaginous or bony basihyal. See lingual plate. Equivalent to the basihyal of Elasmobranchii).
os gulare (plural ossa gularia) = gular plate (the median or paired, dermal, flat bone(s}between the lower jaws of primitive Teleostomes, below the basibranchials. There is a median gular in Amiidae and some Elopidae, Megalopidae and Albulidae, in some Dipnoi there is a second, posterior median plate while others have two pairs of gulars lateral to the median plate, and in Latimeria, Polypterus and Calamoichthys there is a median plate and a lateral plate on each side. Presumably gulars are serially homologous with branchiostegal rays).
os gulare laterale (plural ossa gularia laterale) = lateral gular (a paired dermal bone of the basal throat region in, e.g. Latimeria).
os hypobranchiale (plural ossa hypobranchialia) = hypobranchial (one of a series of deep, paired endochondral bones on the lower part of the gill arch between the ceratobranchials and the basibranchials. May occur on arches 1, 2, 3, 4 and bear dentigerous plates. Salmonidae have only 3 pairs. In Chondrichthyes they are the most ventral paired cartilages, each called cartilago hypobranchialis).
os hypohyale (plural ossa hypohyalia) = hypohyal (the one or two deep, endochondral bones in the hyoid arch between the ceratohyal and the glossohyal. Articulates dorsally with the ceratohyal and ventrally with the basihyal. Lepisosteus has only one while Gadus has two, the dorsal hypohyal or dorsohyal and the ventral hypohyal or ventrohyal).
os hypurale (plural ossa hypuralia) = hypural (one of the flattened, fused bony haemal spines fanning out at the base of the caudal fin and bearing caudal rays. Amia has 10 hypurals, Salmo 7 but in most teleosts the number is reduced or fused into a single structure, the urostyle, q.v.).
os infraorbitale (plural ossa infraorbitalia) = infraorbital bone (one of a series of dermal bones generally below the eye. Name applied to the first six circumorbital bones: infraorbital 1 (lachrymal or preorbital), infraorbital 2 (jugal), infraorbital 3 (true postorbital), infraorbitals 4 and 5, and infraorbital 6 (dermosphenotic). Associated with the infraorbital lateral line. Suborbital bones, q.v., are recognised by some authors as a separate series, sometimes used as a synonym for infraorbital).
os innominatum (plural ossa innominata) = innominate bone (the pelvic fin bone in Gasterosteidae, sometimes a misnomer for the ectocoracoid. Also called pelvic bone, pelvic plate, posterior process, pubic bone and medial plate).
os intercalare (plural ossa intercalaria) = intercalar (a separate sesamoid bone, forming the posterior wall of the otic or auditory capsule, between the prootic, pterotic and the exoccipital and associated with the ventral process of the posttemporal. Also called opisthotic, q.v. and sometimes applied to the autopterotic. Absent in Siluridae and with a foramen for the glossopharyngeal nerve in Gadidae).
os interhyale (plural ossa interhyalia) = interhyal (the deep, endochondral bone between the hyomandibular and symplectic bone and above the epihyal in the hyoid arch. Absent in Dipnoi. Also called stylohyal but not homologous with the stylohyal of Tetrapoda).
os intermusculare (plural ossa intermuscularia) = intermuscular bone (a rib bone lying in the horizontal septum between the epaxial and hypaxial muscles or in the myocommata of the epaxials. See also myorhabdoi, epineurals, dorsal ribs).
os interoperculare (plural ossa interopercularia) = os interoperculum.
os interoperculum (plural ossa interopercula) = interopercle (the paired dermal bone of the lower gill cover below the horizontal arm of the preopercle and in front of the subopercle. Connected to the mandible by a ligament. Absent in Lepisosteus and Siluridae).
os investientium (plural ossa investientia) = membrane bone (a bone which arises directly from connective tissue membranes without cartilaginous precursors. Includes dermal bones, as opposed to cartilage ones. Membrane bones are thin, laminar and located near the surface of the body. When the connective mesenchyme transforms into bone it does not differ histologically from bone which arose from cartilage. Also called achondral, dermal (q.v.), covering and investing bone).
os jugale (plural ossa jugalia) = jugal (a dermal bone below the eye, the second in the circumorbital series, to which the adductor maxillaris muscle attaches its mesial surface. Also used by some authors for the supramaxilla, q.v. and the first suborbital bone or lachrymal, q.v.).
os jugostegale (plural ossa jugostegalia) = jugostegalia (the name given to the numerous rib-like osseus supports in the outer ventral walls behind the branchiostegals of the branchial chamber of the eel, Myrophis. Not regarded as homologous with branchiostegals and considered as structural supports of the prolonged branchial cavity. Other authors regarded them as homologous, defining them as those secondary, multiplied, overlapping and free (from the hyoid arch) branchiostegals found in certain anguilliforms. The term accessory branchiostegal rays is preferred by some authors to jugostegalia, although uncertain as to their homology. Characteristic of the anguilliform familes Echelidae, Ophichthidae and Neenchelyidae. Also called jugostegal rays).
os lacrimale (plural ossa lacrimalia) = lachrymal (the first, paired, dermal bone in the circumorbital series, the largest. Also called preorbital and also spelled lachrimal, lacrimal).
os lacrimojugale (plural ossa lacrimojugalia) = lacrymojugal (a paired dermal bone formed from the fusion of the first two infraorbitals, e.g. in Latimeria and Homalopteridae).
os linguale plattum (plural ossa lingualia plattum) = lingual plate (a dermal toothed bone covering and sometimes fusing with the basihyal, e.g. in Osteoglossidae. Also called glossohyal, dermentoglossum, supralingual or basihyal dental plate).
os maxillare (plural ossa maxillaria) = maxilla (plural maxillae)(the dermal bone forming part of the upper jaw, displaced inwards by the premaxilla in more modern Teleostei. It may bear teeth. Also called maxillary which is also the adjective).
os meckelium (plural ossa meckelia) = coronomeckelian (a small bone on the postero-lateral part of Meckel's cartilage of the lower jaw. Often a point of insertion of the adductor mandibulae muscle. Also called sesamoid angular, supraangular, sesamoid articular, articular sesamoid, splenial, or d bone).
os mentomeckelium (plural ossa mentomeckelia) = mentomeckelian (the ossified tip of Meckel's cartilage. It fuses with the dentary in most Teleostei but is independent in Cyprinidae. Found in Amia and perhaps larval Salmonidae. Also called mentomandibular).
os mesethmoideum (plural ossa mesethmoidea) = mesethmoid (a term misapplied to the ethmoid (q.v.); the fish structure is not homologous with that in mammals).
os mesocoracoideum (plural ossa mesocoracoidea) = mesocoracoid (a paired pectoral girdle endochondral bone between the cleithrum dorsally and the coracoid and scapula ventrally).
os mesopterygoideum (plural ossa mesopterygoidea) = mesopterygoid (endopterygoid (a deep, paired bone on the roof of the mouth lying behind the pterygoid)).
os metapterygoideum (plural ossa metaperygoidea = metapterygoid (the deep, paired, endochondral bone forming the posterior end of the palatoquadrate and connected with the hyomandibular. Absent in many modern Teleostei, it bears teeth in the Albulidae. Also called mesopterygoid, endopterygoid and entopterygoid).
os nasale (plural ossa nasalia) = nasal bone (a paired dermal bone occurring between the premaxilla and the prefrontal, antorbital or lachrymal on either side of the snout and usually enclosing the nares. Lepisosteus has three nasals, prenasal or rostral, adnasal or nasal and premaxillo-nasal or antorbital).
os operculare (plural ossa opercularia) = opercle (the principle and largest, paired dermal bone comprising the upper part of the gill cover above the subopercle. Sometimes used in aging studies).
os operculum (plural ossa opercula) = opercle (the principle and largest, paired dermal bone comprising the upper part of the gill cover above the subopercle. Sometimes used in aging studies).
os opisthoticum (plural ossa opisthotica) = opisthotic (a deep, endochondral bone forming the ventral element of the otic capsule, covering the ampulla of the posterior semicircular canal. Sometimes applied to the autopterotic. Present in fossil Crossopterygii and Actinopterygii, lost in Amia, Lepisosteus and modern Teleostei and therefore the name intercalar is more accurate for these fishes).
os orbitosphenoideum (plural ossa orbitosphenoidea) = orbitosphenoid (a deep, median or paired, endochondral bone underlying the frontal bone forming the floor and walls of the anterior end of the cranium. Visible in the wall of the orbit. Absent in Salmonidae and Gadidae, for example).
os palatinum (plural ossa palatina) = palatine (a paired, endochondral bone on the roof of the mouth lateral to the (pre) vomer. Properly called the autopalatine since it has a double nature, being covered ventrally by the dermal dermopalatine, which is often dentigerous. The palatine is cartilaginous in Lepisosteus and in Amia the dermopalatine is independent, not fused to the autopalatine).
os parasphenoideum (plural ossa parasphenoidea) = parasphenoid (the median dermal bone extending along the base of the cranium, posterior to the prevomer (or vomer). May bear teeth, e.g. in Amia, or molariform teeth, e.g. in Albulidae).
os parietale (plural ossa parietalia) = parietal (a dermal paired bone on each side of the top rear of the head over the auditory region, behind the frontals and partly or wholly separated by the supraocciptal. In Amia and Elopidae both parietals meet in the midline and separate the frontals and the supraocciptal, forming a type of skull called medioparietal. In contrast, a lateroparietal skull has the frontals and supraoccipital meeting in the midline, separating the parietals, e.g. in Gadidae. In an aparietal skull, the parietals are absent, e.g. in Syngnathiformes, Siluruidae).
os parietooccipitale (plural ossa parietooccipitalia) = parietoccipital (dermosupraoccipital (the superficial, paired dermal bone covering the supraoccipital with which it may fuse. In many Teleostei it is a hinge for the skull articulation with the circumorbital ring. Siluridae have a posterior toothed process that secures the nuchal disc. Also called postparietal or dermal supraoccipital).
os pharyngeum inferior (plural ossa pharyngea inferiora) = lower pharyngeal bone (the fifth ceratobranchial, especially that in Cyprinidae and relatives, which is strengthened and tooth-bearing. Also called infrapharyngobranchial dental plate).
os pharyngobranchiale (plural ossa pharyngobranchialia) = pharyngobranchial (the deep, endochondral bone at the top of the gill arch. May bear the upper pharyngeal and a dentigerous plate. May occur on arches 1, 2, 3, 4. Also called super-pharyngeals or superior pharyngeals. Suprapharyngobranchials are never associated with teeth while infrapharyngobranchials may be associated with dermal plates bearing teeth).
os pleurosphenoideum (plural ossa pleurosphenoidea) = pleurosphenoid (misnomer for pterosphenoid, q.v., since it is not homologous with the reptilian pleurosphenoid).
os postcleithrum (plural ossa postcleithra) = postcleithrum (a dermal bone of the pectoral girdle posteroventral to the cleithrum which supports it dorsally. There may be one to several postcleithra (absent in some species). Also called metacleithrum and postclavicle).
os postorbitale (plural ossa postorbitalia) = postorbital (behind the orbit or eye; a bone in the series behind the eye, part of the infraorbital series. They are SO3, SO4, SO5 and SO6 or IO3.....IO6. IO6 is also called the dermosphenotic, q.v.).
os posttemporale (plural ossa posttemporalia) = posttemporal (the superficial, Y-shaped dermal bone connecting the pectoral girdle with the skull, namely the epiotic or supraoccipital (upper part of the bone) and the opisthotic (in primitive fishes) or the intercalar (in modern fishes)(lower part of the bone). Traversed by the posttemporal lateral line canal. Also called suprascapula, suprascapular, supracleithrum I and supraclavicle I).
os præarticulare (plural ossa præarticularia) = prearticular (1) the paired dermal bone of the lower jaw covering the articular mesially, bearing teeth and having a well-developed coronoid process, (2) coronoid (a paired dermal bone bearing teeth located on the upper edge of Meckel's cartilage. One pair is found in Acipenseridae and two pairs in Amia and Lepisosteus. Also called presplenial, splenial and intradentary)).
os præethmoideum (plural ossa præethmoidea) = pre-ethmoid (one of the paired deep bones lying above the vomer in Amia and Esox. Similar bones occur in Catostomidae and Cyprinidae. Formerly called septomaxilla but not homologous with that bone in tetrapods).
os præfrontale (plural ossa præfrontalia) = prefrontal (a superficial, paired, dermal bone lying in front of the eye between the lacrymal and first supraorbital and covering and fusing with the parethmoid; a term often used for the lateral ethmoid or a portion of the lateral ethmoid of dermal origin).
os præmaxilla (plural ossa præmaxillæ) = premaxilla (one of the paired, superficial, usually toothed, dermal bones of the upper jaw, proximal or anterior to the maxillaries; in primitive Teleostomi they comprise the middle, in more advanced forms they may comprise the whole, of the oral edge of the upper jaw. Teeth may be present. In Diodontidae, the premaxillae are ankylosed and form a single bone. Absent in Chondrostei. In Holostei (Lepisoteus and Amia) the bone has two ossification centres and therefore is a double bone. Holostei and Teleostei have an ascending process anteriorly but these may not be homologous. Posterior to the ascending process in Teleostei there may be an articular and a postmaxillary process, and a posterior extension, the caudal process. Also called premaxillary, surmaxillary, bimaxillary or intermaxillary).
os prænasale (plural ossa prænasalia) = prenasal (an anterior dermal bone near the snout tip, bearing a sensory canal. Also called rostral).
os præoperculum (plural ossa præopercula) = preopercle (the L-shaped dermal bone which lies in front of the gill cover and which bears the upper part of the preoperculo-mandibular lateral line canal. It may bear spines or fine teeth. It belongs to the suspensorium rather than the opercular series and acts to prevent the suspensorium from moving laterally).
os præorbitale (plural ossa præorbitalia) = preorbital (the usually large bone lying anterior and slightly ventral to the eye. Also known as the lachrymal or first suborbital. The preorbital is the first of the circumorbital series. In Lepisosteus comprises 6-8 ossicles, joined by teeth and forming the border of the upper jaw. Also refers to the area anterior to or below the eye).
os prævomere (plural ossa prævomeria) = prevomer (a frequently toothed median or paired dermal bone in the middle of the roof of the mouth covering the ethmoid ventrally and in front of the parasphenoid. Often incorrectly called vomer, but this bone in mammals is not homologous with the bone in fishes).
os priapium (plural ossa priapia) = the bones of the priapium, q.v.
os proethmoideum (plural ossa proethmoidea) = proethmoid (one of the paired dermal bones resting behind on the frontals and in front on the cartilage above the prevomer, e.g. in Esocoidei).
os prooticum (plural ossa prootica) = prootic (the anterior, deep dermal bone of the otic capsule. In Amia it is the only bone of the otic capsule).
os pterosphenoideum (plural ossa pterosphenoidea) = pterosphenoid (the paired, deep, endochondral bone roofing the skull lying under the frontal, and posterior to the orbitosphenoid. Miscalled alisphenoid and pleurosphenoid but these bones in mammals and reptiles respectively are not homologous).
os pteroticum (plural ossa pterotica) = pterotic (the paired, deep, endochondral bone and the superficial dermal bone covering it in Actinopterygii forming the lateral roof of the skull between the parietal and the hyomandibular, covering the ampulla of the horizontal semicircular canal. Also called autopterotic, which is strictly used for the endochondral element. In Amia it is a paired dermal bone carrying a sensory canal and occupying the dorsal side of the otic capsule. Also called squamosal or squamous but this tetrapod bone is not homologous (but see squamosal)).
os pterygoideum (plural ossa pterygoidea) = pterygoid (a paired dermal bone between the autopalatine and the endopterygoid in the roof of the mouth (of the palatoquadrate). See also ectopterygoid).
os quadrato-jugale (plural ossa quadrato-jugalia) = quadratojugal (a paired dermal bone behind the quadrate, e.g. in Lepisosteus and Acipenseridae. It may be an independent ossification, e.g. in Salmo and Syngnathus. Sometimes called interopercle or preopercle from its position).
os quadratum (plural ossa quadrata) = quadrate (a paired, triangular, deep, endochondral bone on which the mandible hinges, connecting the lower jaw to the palatine and hyoid arches. During evolution becomes the incus bone of the inner ear of mammals).
os radiiferum (plural ossa radiifera) = axonost or pterygiophore (the cartilage or bone on the outer end of which sit the median fin rays or spines, sometimes the proximal pterygiophore).
os radiale (plural ossa radialia) = radial (a bony or cartilaginous support for a fin ray or spine. Usually three - the proximal, middle and distal radials. If the proximal radial is notably larger it is spoken of as a basal. Teleosts have only one row of radials between the fin rays and the supporting skeleton and these are called actinosts. More primitive fishes have more, e.g. Polyodon has 13, Acipenser has 9).
os retroarticulare (plural ossa retroarticlularia) = retroarticular (the triangular, endochondral, dermal or mixed origin bone on the back, hind corner of the lower jaw. Often called the angular, Bridge's ossicle a, lower articular or angulo-retroarticular).
os rostrale (plural ossa rostralia) = rostral bone (the paired superficial dermal bone covering the ethmoid anterior to the eye in Holostei).
os scapulum (plural ossa scapula) = scapula (the upper, paired endochondral bone on which the pterygials, actinosts or radials of the pectoral fin rest. It articulates ventrally with the coracoid an anteriorly with the cleithrum. A notch on the lower edge of the scapula matches a similar notch on the coracoid to frame the scapular foramen).
os scleroticale (plural ossa scleroticalia) = sclerotic bone (one of a series of bones in the sclera of the eye, e.g. in Salmo there are anterior and posterior sclerotic bones, in Gasterosteus dorsal and posterior, and in Xiphias the entire sclera ossifies with two openings, one for the cornea and one for the optic nerve).
os sphenoticum (plural ossa sphenotica) = sphenotic (a deep bone below the frontal, above the pterosphenoid (or alisphenoid) and under the dermosphenotic. Also called autosphenotic).
os spleniale (plural ossa splenialia) = splenial (a dermal bone carrying a sensory canal, e.g. in Amia. Also called sesamoid angular or submandibular).
os squamosum (plural ossa squamosa) = squamosal (a paired endochondral bone found in Latimeria but incorporated in the preopercle of modern Actinopterygii. Also a term misapplied to the pterotic in fishes).
os suboperculare (plural ossa subopercularia) = subopercle (the paired dermal bone lying below the opercle in the gill cover. Also called subopercular and suboperculum).
os suboperculum (plural ossa subopercula) = subopercle (the paired dermal bone lying below the opercle in the gill cover. Also called subopercular and suboperculum).
os suborbitale (plural ossa suborbitalia) = suborbital (below the eye. Name applied to the first six circumorbital bones: suborbital 1 (lachrymal or preorbital), suborbital 2 (jugal), suborbital 3 (true postorbital), suborbitals 4 and 5, and suborbital 6 (dermosphenotic). Also called infraorbital bones. Associated with the infraorbital lateral line. Sometimes reserved for a chain of small bones below the infraorbitals and unrelated to the infraorbital sensory canal, e.g. in palaeoniscoids, usually absent in advanced fishes).
os supraangulare (plural ossa supraangularia) = supraangular (coronomeckelian (a small bone on the postero-lateral part of Meckel's cartilage of the lower jaw. Often a point of insertion of the adductor mandibulae muscle. Also called sesamoid angular, sesamoid articular, articular sesamoid, splenial, os meckeli or d bone)).
os supracleithrum (plural ossa supracleithra) = supracleithrum (the paired dermal bone of the secondary pectoral girdle above the cleithrum and below the posttemporal. Also called hypercleithrum).
os supraethmoideum (plural ossa supraethmoidea) = supraethmoid (one of the paired dermal bones above the ethmoid, anterior to the frontals. Also called dermethmoid, dermal ethmoid, mesethmoid, dermal mesethmoid rostral).
os supramaxillare (plural ossa supramaxillaria) = supramaxilla (the dermal bone(s) on the upper side of the posterior end of the maxilla. Salmonidae have one supramaxilla while Sternoptychidae have two. Lost in more advanced Teleostei. Also called supramaxillary, surmaxilla, surmaxillary, malar and jugal).
os supraoccipitale (plural ossa supraoccipitalia) = supraocciptal (a median, mixed-origin bone at the upper rear end of the cranium, often bearing a crest, and forming the upper edge of the foramen magnum. In most bony fishes its origins are from the ossification of the otic roof (tectum synoticum) and the connective median septum separating the anterior trunk muscles. Absent in Chondrostei and Holostei).
os supraorbitale (plural ossa supraorbitalia) = supraorbital bone (one of the 1-3 dermal bones of the circumorbital series forming, when present, the dorsal margin of the orbit and lacking sensory canals. The fossil Pholidophoridae had 3 supraorbitals, many modern fishes have 1 or 2, Amia and more advanced Teleostei have none).
os suprapharyngobranchiale (plural ossa suprapharynygobranchialia) = suprapharyngobranchial (pharyngobranchial (the deep, endochondral bone at the top of the gill arch. May bear the upper pharyngeal and a dentigerous plate. May occur on arches 1, 2, 3, 4. Also called super-pharyngeals or superior pharyngeals. Suprapharyngobranchials are never associated with teeth while infrapharyngobranchials may be associated with dermal plates bearing teeth)).
os suprapræoperculum (plural ossa suprapræopercula) = suprapreopercle (a small, paired dermal tube bone carrying the lateral line canal across the gap between the preopercle and supratemporal, often absent. Also called supratemporal, subtemporal and suprapreoperculum).
os suspensorium (plural ossa suspensoria) = a suspensory bone of the Weberian apparatus, q.v., being a modified fourth rib and parapophysis supporting the anterior gas bladder and dorsal mesentery.
os symplecticum (plural ossa symplectica) = symplectic (the small, paired, deep, endochondral bone joining the quadrate and the hyomandibular and supporting the interhyal in the hyostylic jaw (q.v.). It is cartilaginous in Acipenser and absent in Siluroidei and Anguilloidei).
os tabulare (plural ossa tabularia) = tabular bone (extrascapula (a small bone bordering the posterior margin of the skull roof in primitive Teleostomi. These bones apparently originate from enlarged scales. One of a series of from 2-8 bones known variously as cervicals, nuchals, postparietals, scale bones or supratemporals. Often small and thin dermal bones on the nape or above the opercular membrane related to the supratemporal sensory canal)).
os urodermale (plural ossa urodermalia) = urodermal (paired, thin dermal bones at the rear of the caudal fin skeleton, derived from scales).
os urohyale (plural ossa urohyalia) = urohyal (a flat, median, deep, endochondral bone below the ceratohyal; a tendon bone arising in the septum between the longitudinal muscles of the isthmus. Absent in such primitive fishes as Lepisosteus. Also called clidost, episternal, interclavicle and parahyoid).
os uroneurale (plural ossa uroneuralia) = uroneural (one of the paired, elongate, endochondral bones projecting from the lateral surfaces of the urostyle).
os vomere (plural ossa vomeria) = vomer (prevomer, a frequently toothed median or paired dermal bone in the middle of the roof of the mouth covering the ethmoid ventrally and in front of the parasphenoid. Incorrectly called vomer).
oscillatory swimming = use of the paired fins, pectorals and pelvics, to generate highly manoeuvrable movement. See also undulatory swimming.
osel = ossil.
O'Shaugnessy hook = a hook with the point bent slightly outward, similar to the sproat and Limerick.
osmoregulation = maintenance of a proper balance of salts and water within an organism. Freshwater fish regulate hyperosmotically as they tend to lose salts and take up water. They have a glomerular kidney which secretes very dilute urine (up to 20% of body weight each day), kidney tubules are impermeable to water, sodium ions are actively pumped from the distal kidney tubules and across membranes of chloride cells (q.v.) in the gills while chloride ions passively follow the gradient established, and the sodium and potassium pump across the gills involves an exchange of ammonium ions for sodium or potassium ions so ammonia is eliminated while salts are gained. Marine fish regulate hypo-osmotically as they tend to gain salts and lose water. They have an aglomerular kidney which produces very little urine while secreting magnesium and sulphate ions, seawater is drunk copiously (up to 12% of body weight per day), sodium ions are actively pumped from the gut to body fluids and chlorine ions and water follow passively, the gut is relatively impermeable to magnesium and sulphate ions, the chloride cells actively secrete sodium and chlorine ions follow, and the gill membranes are relatively impermeable to water. Sharks use urea to maintain internal osmotic levels above sea water while excess salt from food is excreted via a rectal gland, (q.v.). Fish living in euryhaline waters have a glomerular kidney that can be shut down by arteriole constriction and chloride cells that can switch between taking up salt and secreting it. Based on www.csuchico.edu/~pmaslin/ichthy/xcrtn.html, downloaded 29 December 2003.
ossa = plural of os.
ossa actinosta = plural of os actinostum.
ossa adnasalia = plural of os adnasale.
ossa alisphenoidalia = plural of os alisphenoidale.
ossa angularia = plural of os angulare.
ossa antorbitalia = plural of os antorbitale.
ossa articularia = plural of os articulare.
ossa auditoria = plural of os auditorium.
ossa autopalatina = plural of os autopalatinum.
ossa autopterotica = plural of os autopteroticum.
ossa autosphenotica = plural of os autosphenoticum.
ossa basibranchialia = plural of os basibranchiale.
ossa basihyalia = plural of os basihyale.
ossa basioccipitalia = plural of os basioccipitale.
ossa basipterygia = plural of os basipterygium.
ossa basipsphenoidea = plural of os basisphenoideum.
ossa branchiopercula = plural of os branchioperculum.
ossa branchiostegalia = plural of os branchiostegale.
ossa circumorbitalia = plural of os circumorbitale.
ossa cleithra = plural of os cleithrum.
ossa coracoidea = plural of os coracoideum.
ossa coronomeckelia = plural of os coronomeckelium.
ossa coxae = plural of os coxa.
ossa dentalia = plural of os dentale.
ossa dermoarticularia = plural of os dermoarticulare.
ossa dermopalatina = plural of os dermopalatinum.
ossa dermosphenotica = plural of os dermosphenoticum.
ossa dermosupraoccipitalia = plural of os dermosupraoccipitale.
ossa ectocoracoidea = plural of os ectocoracoideum.
ossa ectopterygoidea = plural of os ectopterygoideum.
ossa epihyalia = plural of os epihyale.
ossa epioccipitalia = plural of os epioocciptale.
ossa epiotica = plural of os epioticum.
ossa epuralia = plural of os epurale.
ossa ethmoidalia = plural of os ethmoidale.
ossa ethmoidea lateralia = plural of os ethmoideum laterale.
ossa frontalia = plural of os frontale.
ossa glossohyalia = plural of os glossohyale.
ossa gularia = plural of os gulare.
ossa gularia laterale = plural of os gulare laterale.
ossa hypobranchialia = plural of os hypobranchiale.
ossa hypohyalia = plural of os hypohyale.
ossa hypuralia = plural of os hypurale.
ossa infraorbitalia = plural of os infraorbitale.
ossa innominata = plural of os innominatum.
ossa intercalaria = plural of os intercalare.
ossa interhyalia = plural of os interhyale.
ossa intermuscularia = plural of os intermusculare.
ossa interopercularia = plural of os interoperculare.
ossa interopercula = plural of os interoperculum.
ossa investientia = plural of os investientium.
ossa jugalia = plural of os jugale.
ossa jugostegalia = plural of os jugostegale.
ossa lacrimalia = plural of os lacrimale.
ossa lacrimojugalia = plural of os lacrimojugale.
ossa lingualia plattum = plural of os linguale plattum.
ossa maxillaria = plural of os maxillare.
ossa meckelia = plural of os meckelium.
ossa mentomeckelia = plural of os mentomeckelium.
ossa mesethmoidea = plural of os mesethmoideum.
ossa mesocoracoidea = plural of os mesocoracoideum.
ossa mesopterygoidea = plural of os mesopterygoideum.
ossa metaperygoidea = plural of os metapterygoideum.
ossa nasalia = plural of os nasale.
ossa opercularia = plural of os operculare.
ossa opercula = plural of os operculum.
ossa opisthotica = plural of os opisthoticum.
ossa orbitosphenoidea = plural of os orbitosphenoideum.
ossa palatina = plural of os palatinum.
ossa parasphenoidea = plural of os parasphenoideum.
ossa parietalia = plural of os parietale.
ossa parietooccipitalia = plural of os parietooccipitale.
ossa pharyngea inferiora = plural of os pharyngeum inferior.
ossa pharyngobranchialia = plural of os pharyngobranchiale.
ossa pleurosphenoidea = plural of os pleurosphenoideum.
ossa postcleithra = plural of os postcleithrum.
ossa postorbitalia = plural of os postorbitale.
ossa posttemporalia = plural of os posttemporale.
ossa præarticularia = plural of os præarticulare.
ossa præethmoidea = plural of os præethmoideum.
ossa præfrontalia = plural of os præfrontale.
ossa præmaxillæ = plural of os præmaxilla.
ossa prænasalia = plural of os prænasale.
ossa præopercula = plural of os præoperculum.
ossa præorbitalia = plural of os præorbitale.
ossa prævomeria = plural of os prævomere.
ossa priapia = plural of os priapium.
ossa proethmoidea = plural of os proethmoideum.
ossa prootica = plural of os prooticum.
ossa pterosphenoidea = plural of os pterosphenoideum.
ossa pterotica = plural of os pteroticum.
ossa pterygoidea = plural of os pterygoideum.
ossa quadrato-jugalia = plural of os quadrato-jugale.
ossa quadrata = plural of os quadratum.
ossa radiifera = plural of os radiiferum.
ossa radialia = plural of os radiale.
ossa retroarticlularia = plural of os retroarticulare.
ossa rostralia = plural of os rostrale.
ossa scapula = plural of os scapulum.
ossa scleroticalia = plural of os scleroticale.
ossa sphenotica = plural of os sphenoticum.
ossa splenialia = plural of os spleniale.
ossa squamosa = plural of os squamosum.
ossa subopercularia = plural of os suboperculare.
ossa subopercula = plural of os suboperculum.
ossa suborbitalia = plural of os suborbitale.
ossa supraangularia = plural of os supraangulare.
ossa supracleithra = plural of os supracleithrum.
ossa supraethmoidea = plural of os supraethmoideum.
ossa supramaxillaria = plural of os supramaxillare.
ossa supraoccipitalia = plural of os supraoccipitale.
ossa supraorbitalia = plural of os supraorbitale.
ossa suprapharynygobranchialia = plural of os suprapharyngobranchiale.
ossa suprapræopercula = plural of os suprapræoperculum.
ossa suspensoria = plural of os suspensorium.
ossa symplectica = plural of os symplecticum.
ossa tabularia = plural of os tabulare.
ossa urodermalia = plural of os urodermale.
ossa urohyalia = plural of os urohyale.
ossa uroneuralia = plural of os uroneurale.
ossa vomeria = plural of os vomere.
ossel = 1) gill net (Scotland).
ossel = 2) norsel (a short piece of line on a drift net used to attach the hanging line to the head or float line at regular intervals).
osseus = bony; of or pertaining to bone.
ossicle = small bone, e.g. Weberian ossicles, ossicles of Gemminger.
ossicula auditus = bones of the ear.
ossiculith = a minute (0.05-0.5 mm) irregular, plano-convex, ellipsoidal calcareous concretion from the labyrinth of Teleostomes. Usually formed in the sacculus adjacent to the external side of the sagitta or in the lagena. Also used for statoconia, q.v.
ossify (ossification) = to become bony.
ossil = a short line to which a hook is attached (Shetland Isles dialect).
osteoblast = a cell which deposits calcium salts and forms bone, the precursor cells of osteocytes. Osteoblasts migrate to centres of bone formation during early development.
osteoclast = a bone cell which is involved in bone resorption, may be mononucleated in fish.
osteocrania = plural of osteocranium.
osteocranium (plural osteocrania) = the bony part of the skull, becoming more developed as the cartilaginous elements ossify during development or evolution.
osteocyte = a cell derivid from an osteoblast responsible for building the hard matrix of bone (supportive fibres impregnated with calcium hydroxyapatite). Osteocytes are usually found in lacunae embedded in the hard matrix but may be superficial to the matrix, e.g. in some fish scales.
osteoderm = scute; dermal bone lying over the epidermis as armor or ornamentation.
osteodont = a type of tooth vascularisation in Chondrichthyes without an internal pulp cavity but by scattered tiny cavities and canals penetrating the osteodontine layer of the root and the internal crown material (Herman et al., 1994).
osteology = study of the structure and development of bones.
ostium = a small opening into a duct or space.
ostolite = fossilised otoliths.
ostraciform = a type of undulatory locomotion in which the body is inflexible and only the tail undulates, e.g. in Ostraciidae. See also anguilliform, carangiform, labriform, thunniform.
ostracin = ostracitoxin.
ostracitoxin = the fish poison secreted into the water by fishes of the genus Ostracion (Ostraciontidae). The poison is heat stable, non-dialysable, hemolytic, and non-protein in nature.
ostracophil = 1) a reproductive guild (q.v.) of snail loving, referring to small members of some African Cichlidae that live in empty snail shells.
ostracophil = 2) a reproductive guild (q.v.) of snail loving, but referring to fish hiding eggs in invertebrates. Eggs are deposited by an ovipositor inside clams but also in crabs or ascidians. The eggs have large, dense yolks, lobes or unculi, photophobia prevents expulsion of free embryos, and there are large embryonic respiratory plexuses and carotenoids, e.g. the cyprinid Rhodeus sericeus.
ostracophilous = adjective for ostracophil.
otarena (plural otarenae) = a mineral particle entering through the endolymphatic pore and combining with calcareous granules to form the otoconia in cartilaginous fishes.
otarenae = plural of otarena.
other fish to fry = other matters to attend to, other concerns or interest to pursue. A variant is bigger fish to fry.
other jal = a large cast net in Bengal, India.
otic = relating to hearing, to the ear.
otic capsule = the skeleton surrounding the inner ear or otic vesicle, composed of the prootic, opisthotic, exoccipital, and supraoccipital.
otic region = the skull area containing hearing and equilibrium organs and including endochondral bones (autosphenotics, autopterotics, opisthotics, epiotics), dermal bones (intercalaries, pterotics) and mixed origin bones (sphenotics, prootics).
otic shelf = the basioccipital is divided on either side of the basicranial fenestra to form two shelves in Sarcopterygii. The jugular vein runs along the top of these shelves toward the intracranial joint.
otic vesicle = an epithelial sac behind the fifth rhombomere forming the semicircular canals dorsally and the otolith organs ventrally.
otoccipital = the area of the posterior braincase containing the otic and occipital regions in Sarcopterygii.
otoconia = plural of otoconium.
otoconium (plural otoconia) = ear dust; a minute transparent calcite crystal with well developed faces secreted within the labyrinth and mixed with mineral particles or otarenae.
otocyst = a cyst or large vesicle that contains the otoliths. Divided into an upper portion with three semicircular canals and the utricle and a lower or vestibular portion containing the saccule and the lagena.
otolin = a protein comprising 0.2-10.0% of the otolith.
otolith = a free body in the inner ear used for perception of acceleration including gravity. Composed of aragonite, a form of calcium carbonate, with up to 10% otolin, a protein. The lapillus lies in the utricle, the sagitta in the saccule, and the asteriscus in the lagena. Also called statoliths or ear stones, and incorrectly ear bone. See otoconium, marginaria and jewellery.
otolithometry = age estimation from zones in the otoliths.
otolithi = plural of otolithus.
otolithus (plural otolithi) = otolith.
otoro = the fattest form tuna from the lower belly as served in a sushi restaurant. See chutoro.
otter = 1) a short weighted plank with fish lures, controlled from shore and tending to shear outwards when pulled through the water.
otter = 2) paternoster rig (a fishing rig where the hooklength branches from the mainline. Various styles exist and may have rigid wire branches with several hooklengths. St. Peter is supposed to have used a paternoster ("our father") rig to catch fish, hence the name).
otter = 3) the barb of a hook, in reference to those used by poachers since the barb was as apt at catching fish as otters.
otter = 4) a piece of wood or metal attached to a fishing line and manipulated to disengage the hook if it becomes entangled under water.
otter board = 1) a large, heavy, flat piece of wood and metal on each side of the mouth of an otter trawl; the boards plane or shear through the water and keep the net mouth open. Also called otter door, trawl door, trawl board. The term is also used for any shearing device used to separate lines or drive a line deeper in the water. Various models and designs exist.
otter board = 2) originally a spiked board used by poachers. It was trailed in the water and made to rear like an otter. Salmon were attracted to it and impaled on the spikes.
otter board stow net = a bag net with two wings, one connected to the river bank and the other to a floating otter board. The otter board keeps the mouth of the net open. The otter board can be manipulated to close the mouth of the net to allow boats to pass.
otter fishing = use of trained otters to catch fish in China. The otter is muzzled to prevent it eating the fish and is tied by a line to its trainer. The otter may catch the fish or chase them into nets which are then hauled out with the otter and the captured fish, cf. cormorant fishing. Also carried out in India, Burma, Malaysia, Thailand Sumatra and Sri Lanka, as well as in various parts of Europe, central and south America.
otter trawl = a towed net that strains demersal fish out of the water. Rectangular otter boards of wood or steel on the tow ropes plane through the water and help keep the mouth open and give the trawl its name; floats on the headrope and weights on the ground line also assist in this.
otter twin trawl = two trawl nets working together with a single pair of otter boards and the inner wings attached to a sledge.
ouananiche = land-locked Atlantic salmon, Salmo salar.
oulgit = tainted fish or meat (Shetland Isles dialect).
ounce = 28.3495 g (avoirdupois, abbreviated as oz), 29.573 g water (fluid ounce, abbreviated as fl oz), 28.413 cm3 (Imperial fluid ounce, abbreviated as fl ozBI), 31.103 g (troy ounce, abbreviated as oz tr).
out of the hettle, into the kettle = a Scottish expression used to impress a purchaser with the idea that the fish is perfectly fresh, hettle being a rocky bottom lying between the roadstead and the shore on the Firth of Forth.
out migration = the seasonal migration of salmonids and other fishes from a stream to a lake or the sea, e.g. American shad, Alosa sapidissima.
out sea = deep sea.
outbreeding = in aquaculture, the use of unrelated individuals for reproduction.
outer net = armouring (the outer wall of large mesh netting forming part of a trammel net, q.v. Also called outer wall, outwall, outwalling, trancher, wall, walling, windows).
outer slope = reef slope (the reef seaward of a reef crest). It is sometimes used to represent the lower reef slope.
outer wall = outer net.
outfall = 1) the mouth or outlet of a river, stream, lake, drain or sewer.
outfall = 2) the first salmon falling from a net after a haul.
outfish = to catch more fish than someone else.
outfit = the supplies and gear needed for a man or vessel to prosecute the cod fishery off Newfoundland.
outflow = 1) flowing out, efflux.
outflow = 2) amount of water flowing out.
outgoing loan = a specimen(s) loaned by a museum to another institution or to a researcher.
outgroup = one or more species or other higher monophyletic taxa used to determine polarisation of character states, not including the taxa under study.
outlet = the point where water exits a water body such as a river or lake.
outlet box = monk (a weir structure used to regulate water depth in a pond with a screen to retain fish).
outlier male = a male Oncorhynchus gorbuscha which is smaller than the dominant male, is coloured like a female, and maintains a position to one side of a spawning pair; in this fashion it is able to deposit sperm since the dominant male does not chase it away.
outlying tackle = fishing tackle set in the water.
outmigration = the seasonal migration of salmonids and other fishes from a stream to a lake or the sea, e.g. American shad, Alosa sapidissima.
outplanting = hatchery-reared fish released into streams for rearing and maturing away from the hatchery sites.
outport = a small Newfoundland fishing community.
output controls = management methods aimed at directly limiting fish catch or landings through total allowable catch and quotas.
outrigger = in sea angling, long fibreglass or metal poles used for trolling baits away from the side of a boat.
outrigger trawl = beam trawl (a trawl with short wings and a head rope attached to a metal or wooden beam, 10 m or more long, which keeps the net open horizontally and scrapes the bottom to scoop or startle fish into the net. Metal frames on each end of the beam keep the net open vertically. Beam trawls are used mainly for flatfish (and shrimp)).
outside bend = the curve on the outside line of a water channel or grass bed. In a channel, water depth is greatest there.
outside door = the seaward entrance to a cod trap.
outside stage = a part of the elevated platform on the shore at which fish are landed and prepared for salting in the Newfoundland cod fisheries.
outstafe = a wooden spar used for stretching out a fishing net (Scottish dialect).
outwall = outer net.
outwalling = outer net.
ova = plural of ovum.
oval = a portion of the gas bladder, rich in capillaries, for the absorption of gases. Circular muscles surround the organ and in contraction shut the oval off from the bladder; longitudinal muscles contract to re-expose it.
ovarian = of or pertaining to the ovary.
ovarian artery = a branch of the coeliac artery extending on the left side of the intestine to the dorsal surface of the ovary.
ovarian flap = a flap of tissue or trophonema, a structure in Jenynsia lineata used to absorb histotrophe or ovarian milk.
ovarian milk = histotrophe (or uterine milk, a secretion produced by teleost livebearers for absorptive feeding during fish ontogeny).
ovarian tunic = the membrane covering the ovary.
ovary = the female reproductive organ, producing eggs.
ovary cyst = a disease evidenced by swollen ovaries filled with a yellowish or reddish fluid, of unknown cause.
ovate = egg-shaped.
over stock = to stock with fish in excess of the carrying capacity of the water body.
over yearling = Salmonidae having spent at least one winter in a stream.
over-capacity = a situation where the fishing capacity of a fleet exceeds the availability of fish to it.
over-compensation = a cycling or maturation technique that involves adding much more pollution to an aquarium than fish will create when the tank is fully stocked. This allows stocking with many fish at once.
over-exploitation = rate of exploitation where the resource stock is drawn down below the size that would, on average, support the long term maximum potential yield of the fishery.
over-feeding = excessive feeding in aquaculture leading to abnormalities in development and growth or economic loss.
over-harvested = slaughtered.
over-ripening = unfertilised eggs that are aging and losing quality or viability.
overall mortality rate = an average mortality rate calculated over several length or age classes. May be an average of rates of several classes weighted by the time they have acted or an average of rates of several classes weighted by the number of individuals they have acted on.
overbreeding = aquarium fish may breed or be bred more often than in nature because of the controlled conditions and ready food supply. This may result in stress-related problems and retarded growth. See also precocious breeding.
overcapacity = too many boats chasing too few fish.
overcapitalization = where the amount of harvesting capacity in a fishery exceeds the amount needed to harvest the desired amount of fish at least cost. Too many boats, too much fishing effort. May be addition of new technology rather than new boats.
overcollecting = the capture of fishes where the numbers taken threaten the numbers in the wild, e.g. taking of wild fish for aquaria.
overexploited = a stock abundance that is too low; overfished.
overfall = 1) a structure for the overflow of water, when it reaches a certain level.
overfall = 2) a waterfall.
overfeeding = excessive feeding leading to growth and developmental abnormalities in fish and to the fish not being economically useful.
overfished = a stock exploited beyond which its abundance is considered too low to ensure safe reproduction.
overfishing = 1) a level of fishing effort or fishing mortality such that a reduction of this level would, in the medium term, lead to an increase in the total catch. For long-lived species, overfishing starts well before the stock becomes overfished. See also growth overfishing (average fish caught when too small), economic overfishing (less profitable than it could be) and recruitment overfishing (too few fish left to spawn).
overfishing = 2) illegal fishing, e.g. where more than the quota is taken or other regulations are broken.
overfishing limit = the point at which fishing seriously compromises continued and sustained productivity. May be determined from biological, economic and sociological considerations relevant to that particular fishery.
overflow = water flowing from a reservoir when filled beyond capacity.
overflow prefilter = a device removing particles of algae, detritus, and other small particles before the water enters a trickle filter in aquaria. The floss in the prefilter should be replaced weekly as it soon clogs.
overgrow = 1) to grow too large.
overgrow = 2) to grow over, covering.
overhand knot = a knot tied by hagfish (Myxinidae) at the head and slid down the body to remove excess slime.
overhaul = to pull a fishing-line or net to the surface in order to determine the catch.
overhead cover = shelter protecting fish from overhead; defined by height above water level, usually less than 1 metre.
overprint = offprint.
overstock = to stock in excess of the carrying capacity of a water body.
overturn = circulation of water in lakes or the sea where seasonal temperature changes cause density differentials.
overyearling = Salmonidae having spent at least one winter in a stream.
overwinter = to keep over winter as with brood stock or to survive winter conditions.
oviduct = a tube used to carry eggs away from the ovary.
oviform = egg-shaped.
ovigerous = bearing eggs.
oviparity = production of eggs that hatch and develop outside the body.
oviparous = adjective for oviparity.
oviphagous = adjective for oviphagy.
oviphagy = eating eggs. See also oophagy.
oviposit = to deposit an egg during spawning.
ovipositor = a tubular extension of the female genital opening used to facilitate egg deposition, e.g. in Rhodeus sericeus.
ovo-testes = gonad containing both male and female primary reproductive tissue, e.g. in Centropristes.
ovoid = round or nearly round.
ovophile = members of the Cichlidae where the male excavates a pit in his territory for the eggs. The female takes these eggs into her mouth. In some species, the female attempts to suck up egg dummies, q.v., on the male, the male then releases sperm that the female inadvertently takes into her mouth to fertilise the eggs, e.g. in Aulonocara, Haplochromis and Pseudotropheus.
ovoviviparity = production of eggs that are fertilised and hatch inside the mother but the embryos lack a placental connection to the oviduct or uterus and so do not feed off the mother. The young are born as miniature adults, free-swimming and feeding, e.g. Gambusia holbrooki. See also oviparity, viviparity.
ovum (plural ova) = egg.
oxbow = a u-shaped or looping bend in a river, cut off from the main flow by formation of a new channel.
oxbow lake = a u-shaped section of river isolated from the main channel when a meandering river cuts across the neck of a meander.
oxycercal = a tail fin of tapering form (as opposed to expanded or fan-shaped form (rhipidocercal)), e.g. in Chlamydoselachus, Anguilla, Mastacembelus, Fierasfer.
oxygarum = garum (q.v.) mixed with vinegar.
oxygen factor = the amount of dissolved oxygen necessary to sustain fish.
oxygen minimum layer = a layer in the deep sea where oxygen levels are at their lowest level, usually about 600-900 m.
oxygen-poor layer = tropholytic layer (the deep zone of a lake where food is used faster than it can be produced).
oxygen-rich layer = trophogenic layer (the water layer where photosynthetic production of organic matter exceeds destruction).
oxygenation = any method of introducing air into water.
oxyluciferin = a substance concerned in production of living light (bioluminescence), luciferin being oxidized in the presence of the enzyme luciferase to produce oxyluciferin and light.
Oxyrhynchus = a famous archeaological site at the town of el-Bahnasa on the Nile in Egypt. The Greek name was Oxyrhynchon Polis, meaning "town of the sharp-nosed fish". The town was named for the fish that ate the penis of Osiris in Egyptian mythology. The species of fish is probably a mormyrid. Egyptian priests were forbidden to eat fish.
oxytetracycline = an antibiotic injected into fish that leaves marks on growth structures such as otoliths. When the fish is recaptured, the elapsed time is known and the mark of the antibiotic can be used to validate age estimates.
oyster bar = a shallow reef area where oysters are exposed at low tide; a good fish habitat.
oz = ounce (28.3495 g avoirdupois).
oz tr = troy ounce (31.103 g).
ozle = the line by which cork buoys are attached to a herring net (Scotland).
© Brian W. Coad (www.briancoad.com)