The cod family is found in temperate to cold marine waters, mainly in the Northern Hemisphere, with only one species always resident in fresh water. There are about 31 species in the family. Maximum size is about 1.8 m.

Cods are recognised by the single barbel usually present under the chin; 1-3 dorsal fins and 1-2 anal fins; the caudal fin usually extends around the dorsal and ventral tip of the caudal peduncle; no fin spines; wide gill openings with the branchiostegal membranes free or narrowly attached to the isthmus; 6-8 branchiostegal rays; vomer bone in the roof of the mouth toothed; swimbladder not connected to the auditory capsules and with 2 slender, anterior processes; scales small and cycloid; and an obvious lateral line.

Most cods live on or near the bottom in cold shelf and slope waters in large schools and are of immense commercial importance as food and sport fishes. A few species are found in the deep sea to 1300 m while others live intertidally or enter brackish water. Eggs and larvae are usually pelagic. A long pelagic life, and spawning and feeding migrations, result in the wide distribution of many species. Egg production can exceed 60 million in some species. Adults feed on other fishes and various invertebrates. Cods are the principal food fish consumed by humans as, although herrings (Clupeidae) have a larger catch, most is processed into fish meal. Overfishing continues to be a problem.

Genus Lota
Oken, 1817

This genus has a single species found in North America and Eurasia, rarely in Iran. The characters of the species are therefore the same as for the genus.

Lota lota
(Linnaeus, 1758)

Common names

mahi charb (= fat or greasy fish), lot.

[nalim in Russian; burbot, eelpout].

Systematics

Gadus Lota was originally described from European lakes. Iranian specimens are presumed to be the type subspecies with a long and low caudal peduncle and high meristic counts (Pivnička, 1970). Subspecies defined on numbers of pyloric caeca are not accepted since there is clinal and size variation (Kottelat, 1997).

Key characters

The chin barbel and 2 dorsal fins, both lacking spines, are distinctive.

Morphology

First dorsal fin rays 7-16, second dorsal fin rays 60-94, anal fin rays 58-86, pectoral fin rays 15-24, pelvic fin rays 5-10, gill rakers 4-12, short, rounded and spinulose, discrete or almost reaching the base of the adjacent raker when appressed, pyloric caeca 21-67, and vertebrae 50-72. The head is flattened, the anterior body rounded and the posterior body compressed. Scales on the body are minute, cycloid, embedded, with few circuli and no radii, and extend onto fin bases and gill covers, and to the level of the nostrils on the head. The second pelvic fin ray is elongated. The anterior nostril is a barbel-like tube. The gut has numerous pyloric caeca, and anterior and posterior loops. The chromosome number is 2n=48 (Klinkhardt et al., 1995).

Sexual dimorphism

Unknown.

Colour

Overall colour is a yellowish to olive-green to dark brown and may be black, with large light blotches on the head, body and vertical fins. The belly is yellow to white and may be finely spotted. All fins are strongly mottled. Mottling is most evident in younger fish; adults tend to become uniformly dark.

Size

Reaches 1.52 m and 34 kg.

Distribution

Found across northern Eurasia and northern North America. Recorded from the lower Safid River in 1921 (Derzhavin, 1934; Berg, 1948-1949) and possibly waters in Gilan but apparently rare in Iran. Berra (1981) omits the distribution in Iran and the southern Caspian Sea basin of Azerbaijan.

Zoogeography

Populations in the Kura River of Azerbaijan may be disjunct from northern populations but their characters have not been thoroughly examined. Abbasov (1980) did not report this species from the Aras River on the northern border of Iran so the Iranian fish, if not strays, may be disjunct even from the southern populations in the Kura River.

Habitat

This species favours cool, clear rivers and lakes where it is most active at night. It hides under rocks and plant roots or in holes in river banks during the day. Young fish remain in shallow weeded areas or rocky streams. It is found only in the lower reaches of rivers along the Iranian shore and does not penetrate upstream (Berg, 1948-1949). This species can tolerate 6‰ and so may enter the Caspian Sea near river mouths. Embryos of this species suffer a 50% mortality if pH rises to 8.0 (Mann, 1996). Fat reserves in the liver are used up in summer when this species is less active.

Age and growth

Maturity is attained at age 2-7 years, varying with habitat, rarely at 1 year for males. Growth is faster in southern populations and maturity is earlier than for northern populations. Maximum life span is 22 years.

Food

Food when young is mostly aquatic insects, crustaceans and molluscs while older burbot feed voraciously on fishes and their eggs and on frogs. Adults do not feed during the spawning period. Most feeding occurs at night. It is reported to be cannibalistic. Glycogene and fat are stored in the liver during spring and autumn feeding periods, allowing the fish to cope with high water temperatures in summer when the fish is less active and feeding is low, even enabling some growth and gonad development (Kottelat and Freyhof, 2007).

Reproduction

Spawning takes place from November to March, even under ice, at temperatures of 0.5-4.0°C on gravel, sand or hard bottoms. Successive matings occur with the male and female swimming head down along the bottom until the male rotates and pushes his belly against hers, releasing eggs and sperm in a cloud. The female beats her tail, mixing the gametes and dispersing the fertilised eggs. One or two females may be surrounded by many males in a spawning ball. The eggs are easily moved by water currents because of a large oil globule in the yolk but gradually sink and lodge in interstices in gravel and sand. Up to 5 million eggs are produced with a diameter about 1.9 mm. About 80 "day degrees" are needed for the eggs to hatch and since they are laid in winter this takes some weeks, e.g. about 6 weeks at 2°C.

Parasites and predators

None reported from Iran.

Economic importance

This species is of economic importance in the former U.S.S.R. and the flesh is said to be excellent as is the liver. The eggs have been used as caviar but are also reported as toxic (Halstead, 1967-1970; Coad, 1979b; see under the genus Schizothorax for symptoms of ichthyootoxism). However it is too rare in Iran to be a food fish and a potential health hazard.

Conservation

Classified as rare to intermediate by Lelek (1987) for Europe. Abdurakhmanov (1962) gives data on only one specimen from the southern Caspian Sea basin, indicative of its rarity. It may be extirpated from Iranian waters.

Further work

Anglers and commercial fishermen should report any captures of this rare species in Iranian waters. Specimens should be preserved for comparison with northern populations.

Sources

Counts are taken from Pivnička (1970).