Lampreys in the family Petromyzontidae are found in cooler waters of the northern hemisphere, with a few related species in other families in the southern hemisphere. Their origins lie at least 300 million years in the past. There are about 37 lamprey species with only 1 recorded from Iran.

Lampreys are jawless fishes, lacking bone in the skeleton and having 7 pairs of pore-like gill openings. The eel-like body has no pectoral or pelvic fins. There are 1 or 2 dorsal fins and a caudal fin. An anal fin-like fold develops in spawning females. The mouth is a suctorial disc armed with rows of horny teeth. There are also teeth on the tongue. The median nostril, or nasohypophyseal opening, is not connected to the mouth. There is a light-sensitive pineal organ or "third eye" behind the nostril. The skin is covered in mucus which is poisonous to fishes and humans. Lampreys are edible if the mucus is cleaned off.

Their tooth arrangement is used in classification and identification along with the number of myomeres (muscle blocks along the body). Both tooth counts and the number of cusps are used, in particular those on the supraoral lamina (bar above the "mouth", the oesophageal opening), the infraoral lamina (bar below the "mouth") and the row of teeth on both sides of the "mouth". There are various series of smaller teeth and of course teeth on the tongue. Larval lampreys lack teeth and are particularly difficult to identify and their determination often requires specialist knowledge. Characters for the larvae include counts of myomeres and pigmentation patterns.

Lampreys have an unusual life cycle. Adults die after spawning and the eggs develop into a larva, known as an ammocoete, which lacks teeth, has an oral hood, eyes covered by skin, a light-sensitive area near the tail, and is a filter-feeder while buried in mud and silt. Fleshy tentacles in the oral hood are used to extract minute organisms from the water, such as algae (desmids and diatoms) and protozoans. After several years (up to 19 but usually 7 or less), the ammocoete transforms into an adult with enlarged eyes, teeth, a different colour and pronounced dorsal fins. The body shrinks during this metamorphosis and adults are only larger than ammocoetes if they feed. The adult may be a parasite on other fishes and marine mammals, or non-feeding. Individuals of a species may or may not be parasitic and different species may be parasitic or non-parasitic. The non-parasitic species are believed to have evolved from a parasitic species so there tends to be closely related parasitic/non-parasitic species pairs.

Parasitic adults feed mostly on other fishes, attaching to their bodies by suction and using their toothed tongue to rasp through the skin and scales to take blood and tissue fragments. Prey is detected by sight but some lampreys attach to hosts during the night. Perhaps this reduces their own predation risks and enables them to approach their quiescent hosts more easily. Lampreys tend to select larger fish as these survive longer and ensure a good food supply. The flow of blood is aided by an anti-coagulant in lamprey saliva called lamphedrin which also serves to break down muscle tissue. The attack may weaken or even kill the host. Weakened fishes are more prone to diseases and the wound provides an easy path of entry for them. The fish (and marine mammal) species parasitised are varied and reflect availability in the habitat.

Marine lampreys enter fresh water to spawn and freshwater species may move into or up streams. The scientific name of the family means "stone sucker" and the adult mouth is used to hold or suck onto stones as well as on prey. This suction enables the lamprey to maintain position in fast-flowing streams when spawning and even to climb over rapids and small waterfalls. Usually spawning occurs in shallow water with a moderate current, a bottom of gravel and nearby sand and silt for the ammocoetes to live in. Either or both sexes build a nest by moving gravel around with their sucking mouths and by thrashing their bodies. A shallow depression is formed, about 0.5-1.0 metre long. Spawning often occurs in groups and several males may attach to a female with the sucking disc. The process takes several days as only a few white to yellow eggs are laid at a time. The eggs are adhesive.

Adult lampreys are usually caught when attached to a host or when spawning. Electro-shocking will force ammocoetes out of their u-shaped burrows to the surface and immobilize adults. They sometimes attach to boats and occasionally to human swimmers when their skin is cool but are easily removed, perhaps because nobody has left a lamprey on their skin long enough to see if the tongue starts rasping flesh!

Genus Caspiomyzon
Berg, 1906

This genus is characterised by having 2 dorsal fins, an oral disc narrower than the body, teeth are generally low and blunt, the supraoral lamina is small, oval and sometimes has 2 tubercles and rarely 2 teeth, the infraoral lamina has 4-6, usually 5, teeth which may be bicuspid at their tips, there are about 8 small teeth of equal size in the transverse lingual lamina, the exolaterals, anterials and posterials are strong and close together, anterior and endolateral circumorals 9-11, usually 11, and 3 long, papillose velar tentacles are present. The first illustration below shows a notch at the end of the second dorsal fin which is an error.

There is a single species in the genus found only in the Caspian Sea basin. Agnathomyzon Gratzianow, 1906 and its subgenus Haploglossa Gratzianow, 1906 are synonyms of Caspiomyzon (Eschmeyer et al., 1996).

Caspiomyzon wagneri
(Kessler, 1870)

Adult

Adult

Ammocoete

Disc

Common names

مارماهي (= mar mahi, meaning snake fish), مارماهي دهان گرد (= marmahi-ye dehangerd, meaning round mouth snake fish), mahi dehangerd, mahi dehangerd daryacheh-ye khazar or dahangerd-e-Daryaye Khazar (= Caspian Sea round mouth fish).

[ilanbaligi or xazar ilanbaligi, djilan-balux or morma in Azerbaijan; kaspiiskaya minoga or Caspian lamprey in Russian; Volga lamprey].

Systematics

The type locality of Petromyzon Wagneri is from the mouth of the Tvertsa to Astrakhan; Oka and Kama rivers and the 3 syntypes (29.0-33.0 cm) are in the Zoological Institute, St. Petersburg (ZISP 31) (Holčík, 1986). The Zoological Museum of Moscow University (ZMMU) has one syntype from the Kura River near Evlakh (P-1393) and one from the Moskva River (P-555) with P-569 from the Volga River near Kazan being lost (Pavlinov and Borissenko, 2001). The Naturhistorisches Museum Wien in 1997 had one specimen listed as "? syntype, ? paratype" (sic) under NMW 61053. Agnathomyzon (Haploglossa) caspicus Gratzianow, 1907 is a synonym.

Key characters

This is the only lamprey species in Iran, easily recognised by the absence of pectoral and pelvic fins, a round, suctorial mouth containing blunt teeth, and 7 branchial openings.

Morphology

Characters of the species are the same as the genus. Trunk myomeres number 53-68 in ammocoetes; and 68(2) or 69(1) in adults from Iran. Ginzburg (1936a) describes ammocoetes from Iran.

Sexual dimorphism

Females reach larger sizes than males and have a smaller urogenital papilla. During the spawning migration, the lamprey undergoes certain morphological changes some of which have been linked to sex of the fish. The teeth become blunt, fin size increases, the dorsal fins become almost united at the base in males, and there is a change in colour. The urogenital papilla length in males increases from a mean of 1.1 mm to 4.9 mm and in females from a mean of 0.6 to 1.7 mm.

Colour

Adults are dark grey with a silvery-white belly. Spawning adults become black on the back and flanks with a grey belly covered with dark oval spots. Ammocoetes are a pale grey to yellowish with a white belly.

Size

Attains 57.5 cm total length and 205.5 g as the adult and 13.0 cm total length as the ammocoete. After metamorphosis of the ammocoete there is a shrinkage in length, the difference between prespawning and spawning adults being on average 22.3% in Iranian samples (Renaud, 1982). There is also a small variety which measures 19-31 cm and can attain sexual maturity at 19.1 cm (forma praecox).

Distribution

Found only in the Caspian Sea and rivers draining to it, in particular the Volga where it had its largest distribution but is now known only as far as the Volgograd Reservoir; also in the Ural, Terek, and Kura rivers. It is recorded in Iran from the upper reaches of the Aras River, and from the Astara to the Gorgan River, including the Anzali Mordab, in most large streams (Derzhavin, 1934; Holčík and Oláh, 1992; Hosseinpour, 1995; Abbasi et al., 1999; Kiabi et al., 1999; Abdoli, 2000). Migrations into the Babol, Gorgan and Sardab rivers are reported by Ghasempouri (1993) and the Sardab and Chalus rivers (Annual Report, 1994-1995, Iranian Fisheries Research and Training Organization, Tehran, p. 28, 1996).

Zoogeography

Known only from the Caspian Sea, its relationships remain uncertain and research is ongoing (Claude B. Renaud, pers. comm., 18 May 2007).

Habitat

The habitat of this species in the southern Caspian Sea proper is unknown although some specimens have been caught in the Caspian at 600-700 m (Jolodar and Abdoli, 2004). Larvae burrow 1-2 cm into the river bottom and favour areas where current is moderate at river bends. They can also be found in the centre of rivers or in backwaters. Fine-grained sand with some ooze and detritus is preferred at all stages of larval growth but larger larvae can also be found in a silt-sand bottom with much plant debris and macrophytes. The ammocoetes select and change habitat according to sediment size as they grow. They prefer depths greater than 3 m as protection against drying out, are mostly shallower than 11 m but as deep as 22 m (Ginzburg, 1970), yet in different rivers or at different times will be concentrated in water of markedly different depths, e.g. 30-85 cm versus 6-8 m.

Spawning migrations up the Volga River used to exceed 1500 km but construction of dams now prevents this. The lamprey migrates in schools with the smaller fish arriving in estuaries first. Larger lampreys migrate more quickly and travel further. The speed varies from 1.9 to 15.9 km/day. The migration is triggered by decreasing water temperature and increasing water level. The strongest migration is reported at 6-11°C. Movement upriver only occurs at night, near the surface when dark and on the bottom when the moon is out. During the day, the lampreys hide among stones. Body fat in the Volga delta was 34% but by the time the fish reached the spawning grounds upriver it had declined to 1-2%. In the Kura River of Azerbaijan, the lamprey migrates at the same time as the Caspian salmon (mahi azad, Salmo trutta caspius) and often attaches to the opercular region of this species. The peak of this run is in December and January. The migration in the Volga takes place from the middle of September to the end of December. Migrating lampreys prefer a current velocity of 0.4-0.6 m/sec and stay close to banks and the bottom. Prespawning adults overwinter among stones or in the substrate of rivers. During winter-spring several individuals may be found coiled in a ball under stones (Askerov et al., 2001). They hardly respond to external stimuli such as noise or being handled. Transformed lampreys migrate to the Caspian Sea. Before breeding, males change colour, increase slightly in size, develop their fins, and become much more active (Askerov et al., 2001).

Age and growth

The growth rates of metamorphosing lampreys and adults are almost unknown. Length and weight decrease but coefficient of condition increases in spawning as opposed to pre-spawning adults. The shrinkage in mean total length is 18-26%. Females are heavier than males up to about 43 cm but past this point males weigh more. There are 3 age groups of larvae in the Volga (Ginzburg, 1970), with average lengths of 3.1 cm, 6.2 cm and 10.1 cm and 2-4 age groups in the Kura. In their fourth year of life they metamorphose to adults after a downstream migration into the Caspian Sea. Adult life span is at least 1 year and 5 months. Maturity is attained in May and the beginning of June in the Volga, and from May to the end of July in the Kura River. Mature lampreys are mostly 35-41 cm in the Volga and 41-46 in the Kura River. The female lamprey dies after spawning but the male may live longer until sperm production ceases.

Food

Abakumov (1959) maintains that this lamprey attacks Caspian salmon (Salmo trutta caspius) based on nineteenth century observations by Kessler (1870a) and Kavraiskii (1896-1897). Lelek (1987) also considers it to be parasitic. The lampreys may only have been using Caspian salmon for transport. Certainly the teeth in this lamprey are blunt, unlike those in lamprey species known to parasitise fishes. In contrast, Holčík (1986) states that it is non-parasitic and Ghasempouri (1993) agrees. Renaud (1982) supposes that adults feed on amphipods since juvenile acanthocephalans (Corynosoma sp.) are found in prespawners. This worm has amphipods as the intermediate host. However, Holčík (1986) thinks that the acanthocephalans are swallowed while the adult lampreys are feeding on the internal organs of dead fish they scavenge. Certainly larvae of Corynosoma strumosum (perhaps correctly C. caspicum: B. Kiabi, in litt., 1994) are found only in the body cavity of fishes. The feeding habits of the adult of this species remain to be confirmed by direct observation. Gut contents include aquatic vegetation in Iran and in the Volga delta. Migratory, transforming and spawning lampreys do not feed. The gut diameter decreases from 2.7 mm in prespawners to 1.4 mm in spawners in Iran (Renaud, 1982). Ammocoetes feed on detritus and diatoms.

Reproduction

Ginzburg (1969; 1970) examined the reproduction of this species below the Volgograd Dam on the Volga River and similar conditions may obtain in Iran. The dam has probably increased fecundity by reducing the length of the spawning migration so that the fish have more energy reserves for egg production. A spawning migration exists from December to May with a peak concentration in the second 10 days of February although the catches declined in April at least in part because of the opening of the spillway of the dam. Before the dam was built the migration from the Caspian Sea passed through the delta from mid-October to mid-December, with a peak in December. The fish migrated when water temperatures reached 10-11°C and moved through channels where the current was strongest. Spawning begins at 15-16°C, usually in early June but sometimes at the end of March through to the beginning of July, and temperatures during spawning are usually 15-23°C. Each female produces up to 60,000 turquoise or blue-green eggs and spawns once in her lifetime. Eggs are ovate and diameter reaches 1.5 mm. The eggs are laid on coarse to fine-grained, turquoise sand at a water depth of 3.5-19.0 m, sometimes shallower. The egg colour is cryptic against the sand substrate. Many eggs are carried downstream by the current. A redd is excavated in sand or gravel by the male or by the female (authors differ on this point) and the lamprey attaches to stones by their suctorial disc. The male attaches to the female's head with his disc and wraps his body around hers. The tails of both fish quiver and eggs and sperm are released at the same time. Females release all their eggs but males may spawn again with other females. Ammocoetes hatch after 8-10 days at 17-23°C. Metamorphosis of ammocoetes occurs at 8.0-11.0 cm in October in Iran.

Parasites and predators

See above under Food. Caspian lampreys are eaten by Silurus glanis, Lota lota, Sander lucioperca, and Huso huso.

Economic importance

This species was consumed and used for oil extraction in the former U.S.S.R. (Thomas, 1961; Ginzburg, 1969). Their fat content is so high that they were once dried and used as candles (Kottelat and Freyhof, 2007) and the high fat level makes them tasty (Askerov et al., 2001). The catch in the Volga-Caspian region was 3,420,000 kg or 33.4 million fish in 1913 but fishing by state organizations ceased after the Volgograd reservoir was constructed. The mean annual catch in Azerbaijan for 1930-1963 ranged from 10 to 269 tonnes. Local fisheries continue but are of little significance. It is not commercially important in Iran for religious reasons but catches of several hundred kilograms can be made in an hour in such rivers as the Gorgan, Babol and Sardab (Ghasempouri, 1993).

Robins et al. (1991) list this species as important to North Americans. Importance is based on its use as food, in textbooks and because it is reputedly ichthyosarcotoxic. Intoxication results from eating the flesh, skin or surface mucus of raw or cooked Caspian lamprey, the location of the toxin being uncertain. A biogenic amine is believed to be responsible. Mucus may cause skin irritations. Poisoning can be avoided by soaking the lamprey in brine as cooking alone is insufficient. Symptoms develop in a few hours and include nausea, vomiting, dysenteric diarrhoea, urge to urinate or defecate without ability to do so, abdominal pain and weakness. Recovery takes several days and treatment is symptomatic (Coad, 1979b). However lampreys lack scales and are not eaten in Iran.

Conservation

The Caspian lamprey has been proposed for inclusion in the "Red Book of the U.S.S.R." which forms the basis for measures to protect species (Pavlov et al., 1985) and is listed as "vulnerable" in Europe by Lelek (1987) and Maitland (1991). It is vulnerable because it migrates into rivers which are polluted and dammed and because of its restricted and declining distribution. These conditions apply particularly in Iran, although there is some evidence for spawning based on captures in the 1990s (Holčík and Oláh, 1992).

Kiabi et al. (1999) consider this species to be near threatened in the south Caspian Sea basin according to IUCN criteria. Criteria include medium numbers, habitat destruction, widespread range (75% of water bodies), absent in other water bodies in Iran, and absent outside the Caspian Sea basin. Mostafavi (2007) lists it as near threatened in the Talar River, Mazandaran.

Further work

The question of adult diet remains unresolved and the general biology of this species in Iran needs to be elucidated.

Sources

The main source of information on this species is the summary by Holčík (1986) which should be consulted for further details on morphology and biology.

Iranian material: CMNFI 1970-0511, 7 ammocoetes, ? 30-82 mm total length, Gilan, Shafa River estuary (37º35'N, 49º09'E); CMNFI 1970-0514, 33 ammocoetes, ? mm total length, Gilan, Shafa River estuary (37º35'N, 49º09'E); CMNFI 1970-0515, 18 ammocoetes, ? 25-98 mm total length, Gilan, Shafa River estuary (37º35'N, 49º09'E); CMNFI 1970-0534, 30 ammocoetes, ? mm total length, Gilan, Shafa River estuary (37º35'N, 49º09'E); CMNFI 1970-0535, 14 ammocoetes, ? mm total length, Gilan, Shafa River estuary (37º35'N, 49º09'E); CMNFI 1970-0545, 1 adult? see photo?, ?mm total length, Gilan, Safid River (37º01'N, 49º38'E); CMNFI 1970-0546, 2 adults, 352.0-355.0 mm total length, Gilan, Safid River (no other locality data); CMNFI 1970-0547,6 adults and 2 ammocoetes, ? photos? mm total length, Gilan, Shafa River estuary (37º35'N, 49º09'E); CMNFI 1970-0585, 3 adults, 406.0-455.0 mm total length, Gilan, Nahang Roga River (37º28'N, 49º28'E); CMNFI 1971-0327A, 1 adult (part of trunk), Gilan, Shafa River estuary (37º35'N, 49º09'E); CMNFI 1979-0787, 11 adults, ?mm total length, Gilan, Nahang Roga River (37º28'N, 49º28'E); CMNFI 1980-0118,8 adults, ? mm total length, Gilan, Gelroudkhan River, tributary of the Anzali Mordab (no other locality data); CMNFI 1980-0119, 10 adults, ? mm total length, Gilan, Gelroudkhan River, tributary of the Anzali Mordab (no other locality data); CMNFI 1980-0139, 44 ammocoetes, ? mm total length, Gilan, Golshan River estuary (37º26'N, 49º40'E).

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