The giant mollusks in the Volga turned out to be from China

(ORDO NEWS) — Biologists have found that giant mollusks, which in recent years are often found in the lower reaches of the Volga, are of Chinese origin. Ivan Bolotov, Director of the Center for Comprehensive Arctic Studies of the Ural Branch of the Russian Academy of Sciences, told TASS about this.

In 2019, residents of the lower reaches of the Volga increasingly began to find toothless – freshwater mollusks of the genus Anodonta – up to 25 cm long. Their photos began to appear on social networks, and the media began to write about them. Having learned about this, biologists from Arkhangelsk organized an expedition to the Volga.

“Local scientists commented that these are climate changes, local species have grown, and so on. But local species never grow to 20-25 cm, and it was clear that this was probably an invasion. The genetic sequences of these mollusks were deciphered, and suddenly it turned out, that these are species characteristic of the rivers of China,” Bolotov said.

Scientists have found that in the Volga there are two types of toothless, which cannot be distinguished visually, they differ only genetically. One of them is characteristic of the Yangtze River, and the second lives in the Songhua River, a tributary of the Amur. From the basins of these rivers in the 1960s-70s, biologists moved juvenile fish to the water bodies of Kazakhstan and some republics of the USSR.

“Fish stocking material was brought from China. Among the fish species were silver carp, grass carp and a number of other Far Eastern species. It turned out that juvenile fish were not checked for the presence of any parasites, and Chinese toothless were brought to Kazakhstan and Romania along the way. , – the scientist explained.

In Kazakhstan, mollusks have successfully adapted; they live in the basin of Lake Balkhash. Toothless, most likely, came to Russia in the early 2000s. “Most likely, with fish planting material from Kazakhstan, – explained Bolotov. – They were brought to the basins of the Yenisei, Ob and Volga rivers.”

Giant competitors

In the Yenisei and Ob, the conditions for heat-loving toothless are harsh, in these rivers they live only in a few places, in areas where warm waters are discharged from the thermal power station. And on the lower Volga, mollusks found themselves in a favorable environment. “We found a very unexpected situation that the lower Volga is literally flooded with these mollusks. In some places, their number among all mollusks reaches 20-30%,” Bolotov added.

This posed several problems. Chinese toothless are much larger than the Volga species; they form dense settlements and displace local mollusks and insects, which are food sources for fish, including sturgeon.

In addition, the larvae of these toothless pests parasitize local fish species. As a result, the hosts of these parasites secrete substances that prevent local parasites from developing on them.

According to Bolotov, it is almost impossible to remove the aliens from the Volga, since they have already integrated into the ecosystem. It is now important to find out if the Chinese species have ended up in other rivers in the country. “It’s clear with the lower Volga, but, say, whether there are Chinese toothless in the Moscow region, no one knows. This is a new threat,” the scientist said.

It is important to prevent molluscs from spreading to other rivers – for example, when young fish migrate to water bodies.

Earlier, the spread of Chinese toothless was encountered in European countries, where the mollusks came from Romania. Now scientists are actively monitoring their spread. “We need to develop programs to reduce the number, but at this stage I am not ready to say how this can be technically organized,” Bolotov concluded.

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