Burbot

(Lota lota)

Order: Gadiformes Family: Gadidae

Foto: Lauri Urho

Description: The burbot is a gadoid fish with an elongated, supple body and a tail that forms half of its total body length. The leathery, slimy skin is a mottled greenish yellow flecked with blackish brown spots. The head is flat. Underneath the tip of the lower jaw there is a barbel, which it uses to explore the environment. The burbot has two dorsal fins, the posterior dorsal fin and anal fin extending almost to the tail.

Origin and distribution: The extensive range of the burbot in the northern hemisphere includes cool and temperate freshwaters, but also brackish waters with low salinity. After the latest glaciation, the burbot was probably one of the first species to invade Finnish waters. It occurs as an indigenous species throughout the country in both brackish and fresh waters right up to northernmost Lapland. It is, however, absent from many acidified small lakes and ponds. In the 1900s, it disappeared from some small water systems running through the aluminous, sulphide rich (Littorina origin) soils of the west coast and also decreased in the coastal waters of the northernmost Gulf of Bothnia. Small-scale translocation and hatchery rearing have been practised in the last few decades.

Reproduction: Burbot reach maturity at 5−6 years of age in northern Finland and usually somewhat younger in the south of the country. In mid-winter adults gather to spawn under the ice in streams and on sea and lake shores. The spawning ground is usually with gravel at a depth of no more than 3 m, often at a spot with flowing water. The fertilized eggs, about 1 mm in diameter, drift along near the bottom. Larvae hatch when the ice cover melts and, living on the reserve nutrition of their yolk sacs, spread into the pelagic, where they start to feed on zooplankton. Larvae develop and feed mainly on zooplankton in very shallow water, at a depth of between 0.1 and 0.5 metres.

Diet, growth and migrations: After the larval period, young burbot feed on bottom fauna, spending the day under rocks and in other sheltered spots in warm littoral waters. During their first year of life, burbot reach a length of 10−12 cm. After two years in littoral waters, they move deeper. At 3 years of age, burbot are about 22−25 cm long, and 3−5 years later 35−40 cm long. The biggest burbot live in deeper, colder water and also eat small fishes. Recently, large individuals weighing 6−8 kg have frequently been caught in northern Finland, where they have a long and favourable feeding period thanks to the cold water. The spawning migration is usually quite short. In Finland, it is at its longest on the west coast, where burbot ascend rivers from the sea to spawn.

Fishing and catches: The traditional fishing season is during the spawn in winter. Burbot are caught with trap nets, fish traps and nets and also by ice-fishing. The roe and white flesh of burbot are great delicacies. Statistics put the catch in recent years at over a million kg annually, the bulk being taken in inland waters. In the 1980s, the annual catch was higher, on average 2.5–3.2 million kg.

Vulnerability, threats and management: Climate warming and other environmental changes threaten burbot stocks, especially in southern and western coastal areas. Burbot stocks have also suffered from acidification due to waters draining from aluminous sulphur-rich soils. Eutrophication poses a further threat to burbot. Reproduction problems have been reported from the sea area near the city of Oulu. In some waters, burbot can no longer survive because of the increased water temperature. Stocks have, for example, decreased or disappeared altogether from waters warmed by nuclear power plants. To date, hatchery rearing has been practised on a small scale only. Hatched larvae from artificially fertilized eggs can be reared in ponds with natural food. As a species, the burbot is viable (a least concern species) in Finland.

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