China is now the world’s largest producer of farmed sturgeon, but rampant hybridisation in pursuit of high yields of meat and caviar may put wild sturgeon at risk from escaped or released hybrid fish.
Sturgeon, of which there are 27 species, are amongst the world’s most endangered species of fish. Found in the coastal seas and oceans of the Northern hemisphere, sturgeons migrate up the rivers in Asia, Europe and North America to spawn.
Most of the former sturgeon spawning grounds have now been cut off from the sea by dams, and the populations of sturgeon across the world have been decimated by overfishing, especially for the highly-prized black caviar.
In China, where several species of sturgeon are native, the situation is critical. The Yangtze sturgeon is functionally extinct. The Chinese sturgeon is likely to also be functionally extinct despite years of releasing millions of young captive-bred fish. The populations of other species – the Amur sturgeon, the Kaluga and the Siberian sturgeon, are all on the brink.
The farms
Yet sturgeon is plentiful in China – on sturgeon farms. China has grown into is the largest producer of farmed sturgeon in the world, producing around 100,000 tons of sturgeon per year across a dozen provinces. Young sturgeons are widely sold on pet markets, for as little as 20 yuan (USD 6) each, as seen by the SVIS Initiative.
The CITES listing of all species of sturgeon means that caviar from wild-caught sturgeon can no longer be sold, but caviar from captive bred sturgeon is exempt. Chinese fish farmers have been extremely successful in filling this gap in the market.
China is now the biggest producer and exporter of sturgeon caviar in the world, supplying it to the high-end retailers and restaurants in Europe and North America. As a rule, most sellers of Chinese caviar are very coy about the origin of their product, usually stating “Asia” as the source.
The hybridisation
However, China’s sturgeon farms can potentially pose grave threat to the wild sturgeon. In their quest to boost yields, sturgeon growers in China have been hybridising a variety of species of sturgeon. A lot of the sturgeon stock in China is now of unclear genetic origin. There appears to be no regulation or oversight of sturgeon hybridisation.
While hybridising sturgeon is nothing new – the Soviets have produced “bester”, a cross between the beluga and ship sturgeon, the unprecedented scale of Chinese sturgeon farms and the availability in China of live sturgeon to the public, are very concerning.
A 2022 publication by the researchers at the Fisheries Research Institute of Guizhou Academy of Aquaculture Sciences, confirms the scale of the sturgeon hybridisation problem. Sturgeon farms no longer know with certainty what species or hybrids they have, and a genetic method now needs to be found to tell the sturgeon apart.
This is an extract from the publication:
“As the quantity of farmed sturgeon (in China) grew, problems of deterioration of stock and decline in product quality emerged. As the result, a very large quantity of hybrids of unknown origin appeared. This resulted in random hybridisation of fish with unknown origin on many sturgeon farms. This made worse the problems of mixing of sturgeon stock and the drop in the quality and quantity of juveniles, which restricted the overall development of the sturgeon farming industry. Therefore, the research on identification of Acipenser schrenckii, (Amur sturgeon) Huso dauricus (kaluga) Acipenser baerii (Siberian sturgeon) and their hybrids is of great significance in guiding the production of sturgeon.”
Artificially created hybrids can either be fertile or infertile, and may or may not be adaptable to the local environment. All eventualities, however, can spell trouble for the genetically pure populations of related species.
If hybrids are fertile, hybridisation may drive parent species to extinction through what is known as genetic swamping, where species are replaced by their hybrids.
If the hybrids are infertile or mal-adapted to the local conditions, the extinction of parent species may occur via demographic swamping, where population growth rates are reduced due to the wasteful production of hybrids that do not survive for very long.
The precedent
There is already evidence of wild sturgeon hybridising as a result of human action.
In the Black Sea there are several species of sturgeon, all on the brink of extinction. A study on the sturgeon DNA done by the Georgian scientists on the country’s Rioni river where spawning grounds remain intact, showed hybridisation between the Russian sturgeon (Acipenser gueldenstaedtii) and the stellate sturgeon (A. stellatus).
The scientists concluded that the reason for the hybridisation is the difficulty of finding a mate of the same species. Populations of all species of sturgeon in the Black Sea are now extremely small.
The two parental species – Russian and stellate sturgeon, differ in the number of chromosomes, and their hybrids are therefore likely to be sterile. However, sterility does not prevent the hybrids from spawning and, therefore, competing with sturgeon of pure species, affecting their chances of reproduction and risking reduction of populations of both species even further.
The risk
China already has hundreds of invasive species of fish from every corner of the world. These have been deliberately released or have escaped from the country’s vast aquaculture farms.
It is not known if hybrid sturgeon from fish farms have found their way into China’s waterways, but the possibility of escape or deliberate release of sturgeon hybrids is real. Accounts of people buying live sturgeon can be found on-line.
One 2015 Chinese media report tells the account of woman from Dongying city, on the northern coast of Shandong province - a major producer of farmed sturgeon, who bought on a market a supposedly wild-caught live Chinese sturgeon. The seller claimed the fish came from the nearby Yellow River. The woman then contacted the authorities, as she knew that the species is protected in China.
The local fisheries authorities claimed the sturgeon was most likely be a farmed fish, and possibly a hybrid of Chinese and Siberian sturgeon.
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