The largest freshwater fish in the world

The Beluga Sturgeon Huso huso is the largest freshwater fish in the world – larger than the Mekong giant catfish Pangasianodon gigas! Indeed, it is thought to be the largest freshwater fish that has ever lived. It is an anadromous species native to the Caspian and Black Sea basins but is now critically endangered due to impacts from hydroelectric development, pollution and over-fishing/poaching. Beluga roe is the most expensive type of caviar. Isinglass, which has been used in the production of Guinness, is also made from sturgeon. The Beluga Sturgeon was formerly abundant and undertook extensive migrations on the Volga and Danube – Europe’s largest rivers.

The record Beluga Sturgeon was caught in the Volga estuary in 1827 and weighed 1,571 kg! The photo below is from the Volga River in 1924.

beluga-sturgeon

Beluga sturgeon from the Volga River in 1924.

Djerdap 1 dam (Iron gates) on the River Danube

Djerdap 1 dam (Iron gates) on the River Danube

huso-huso-farmed

Juvenile Beluga Sturgeon Huso huso are farmed and restocked.

The Beluga Sturgeon can live to over a century – so some individuals out there may have been spawned in habitats now blocked by dams built by Stalin on the Volga, and the Iron Gates dams (1972 – 1985) on the Danube. ‘Functionally extinct’ is the term used for species facing problems like this; our similarly long-lived Freshwater Pearl Mussel Margaritifera margaritifera can no longer reproduce in most Irish rivers yet tens of thousands still exist.

The Beluga Sturgeon undertakes major upriver spawning migration to spawn. It enters rivers in the spring and autumn. Fecundity ranges from 0.36-7.7 million ova, however females mature late and only carry eggs only once every 5-7 years. Spawning habitat is located in the main course of large and deep rivers with strong current and on stone or gravel substrate. Juveniles occur in shallow riverine habitats during their first summer. The young Beluga Sturgeon then migrate to the sea where they feed mainly on fish, but also invertebrates.

The Ural River in Kazakhstan is now the only river flowing into the Caspian Sea that does not have a dam that blocks the migration of this great fish

Beluga sturgeon restocking programmes are ongoing but these do not compensate for the loss of natural reproduction and the populations continue to decline. The annual number of fingerlings (over 15cm) released into the Volga is approximately 3 million, with around 20,000 into the Danube. Some natural reproduction of the species remains in the Volga and Ural Rivers. The provision of artificial spawning grounds has been attempted below the Volgograd dam on the River Volga, with limited success. The Ural River in Kazakhstan is now the only river flowing into the Caspian Sea that does not have a dam that blocks the migration of this great fish. This is a key river to secure the survival of this species.

Giant Beluga Sturgeon caught near the town of Tetyushi on the upper River Volga, 1921. This town is located on the banks of the Kuybyshevskoye Reservoir – the largest reservoir in Europe. The reservoir was created by the dam of Zhiguli Hydroelectric Station which was built in the 1950’s. This is perhaps the same fish as in the photo above?

For more information see the following links:-

The sturgeons are a very old group of fishes (over 200 million years old) and make up one of the most primitive lineages of bony fishes. However, most sturgeon species are now endangered. Occasional sturgeon (Atlantic sturgeon Acipenser sturio) have been captured in Ireland, but it is probably unlikely that it ever bred here. Also listen to the Dingle sturgeon story. It was probably also just a vagrant species to UK rivers but there are many records from larger river systems, including the Severn and Trent.

The last remaining population of A. sturio is now in the River Garonne in France. However, it has not spawned in this river since 1994 where dams, pollution and river regulation have degraded and destroyed its spawning sites.

PS: See this news report from April 2017 reporting that an 850 kg Beluga was caught from the Iranian sector of the Caspian Sea.

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