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The freshwater pearl mussel favors the original salmon fish populations of the home river

The freshwater pearl mussel favors the native salmonfish populations of its home river

Frying salmon. Credit: Heidi Kunttu / University of Jyväskylä

Researchers from the University of Jyväskylä, Finland, have found that freshwater pearl mussel larvae survive best in the native salmon population of their home river. Their study was published in Freshwater Biology

The larvae of freshwater pearl mussel live as parasites on the gills of fish. The larvae grow and develop on the gills for 9 to 11 months and then drop to the river bottom like small mussels.

“In our previous studies we have shown that the mussel larvae can only attach to the gills of the salmon or trout, and that in large salmon rivers the best host for the mussel is the salmon and in smaller rivers the trout,” says Professor Jouni Taskinen, director of the Konnevesi Research Station at the University of Jyväskylä and the LIFE Revives project. “In this study, we wanted to find out whether the freshwater pearl mussels have particularly adapted to the salmon population of the home river.”

The study compared salmon and trout rivers by pooling mussel larvae with fish species from the own river and other rivers. The experiments were done in rivers and streams in Lapland, North Ostrobothnia and Kainuu.

The original host fish of the home river is most welcome

The freshwater mussel larvae bonded most effectively especially to the individuals of the salmonfish populations living in the same streams and rivers. The larvae also grew best on the fish of the home river.

“For example, in the upper reaches of Luttojoki in Ivalo, we cross-exposed the fish of Hanhioja and Kolmosjoki with the mussels of both rivers, and the result was clear: the mussel larvae of Hanhioja adhered best to the Hanhioja salmon and the mussel larvae from Kolmosjoki to the Kolmosjoki salmon,” says Taskinen. A third salmon population unknown for both rivers was also used in the experiment, and it was the population to which the larvae adhered least effectively in both rivers.

  • The freshwater pearl mussel favors the native salmonfish populations of its home river

    Freshwater pearl mussels on the riverbed. Credit: Jouni Salonen / University of Jyväskylä

  • The freshwater pearl mussel favors the native salmonfish populations of its home river

    Researchers’ live nets for host fish in a mussel river. Credit: Felix Luukkanen

Extinction of original migratory fish populations threatens mussel

The freshwater pearl mussel is under threat and has disappeared from nature in many places, despite conservation efforts that started in the 1950s. Dams built to produce hydropower have hindered fish migration, resulting in many salmon and trout populations being nearly lost. The loss to the fishing economy caused by hydropower has been compensated by compensating fish stocks. The study results showed that using a stocking population of salmonfish other than the river’s native population may not be as beneficial for the mussel. It also doesn’t help the mussel if the spawning takes place in a marine area and the fish don’t return to spawn in their own rivers.

The freshwater pearl mussel favors the native salmonfish populations of its home river

A microscopic view of the glochidium larvae of freshwater pearl mussel on the gill of a host fish. Credit: Jouni Salonen / University of Jyväskylä

“For the endangered freshwater pearl mussel, it would be important to restore the original fish populations and their natural migration to rivers,” says Taskinen. “If possible, the river’s native salmon population should be favored in compensating fish stocks, and the stockings should be made in the rivers rather than at sea to benefit the freshwater pearl mussel.”

Freshwater mussels can inhibit bacterial diseases

More information:
Jouni Taskinen et al, The endangered freshwater pearl mussel Margaritifera margaritifera shows adaptation to a local salmonid host in Finland, Freshwater Biology (2022). DOI: 10.1111/fwb.13882

Provided by University of Jyväskylä

Quote: The freshwater pearl mussel favors the native salmonfish populations of its home river (2022, June 21), retrieved June 21, 2022 from https://phys.org/news/2022-06-freshwater-pearl-mussel-favors-salmon. html

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