When farmed salmon interbreed with their wild cousins.

As if it wasn’t enough to fight epidemics, algal blooms and even volcanoes, fish farmers must now pay special attention to fugitives. Salmon escaped from fish farms in Norway apparently spread genetic material to wild populations of Atlantic salmon, according to a new study, compromising their reproductive health.

The researchers, based at the Norwegian Institute for Nature Research (NINA), examined more than 20,000 fish in 147 salmon rivers and found widespread genetic introgression – the flow of genetic material from one gene pool to one. other – in 77 of the rivers sampled. Genetic material from farmed salmon – introduced by escapees breeding with non-farmed fish – was present in nearly 50 percent of the wild populations tested.

Escaped farmed salmon interbreed with wild salmon, altering the gene pool. What can this mean?
Visual: iStock.com

“Half of the wild salmon populations in Norway have genetically changed having proportions of farmed salmon, some with up to 40 percent of their genetic makeup being of farm origin, and an average of 6.4 percent. hundred, “said Sten Karlsson, lead author of the study.

Farmed salmon are bred to grow and grow quickly, Karlsson explains. These genetic traits, while important to the commercial success of farmed salmon, do not work as well when mixed with wild populations.

“These traits are not of a favorable nature and the offspring of wild-farmed salmon have inferior survival and physical form,” Karlsson wrote in an email.

An intrusion of farmed salmon genes into wild gene pools compromises the reproductive success of wild salmon, his study warns. According to a 2008 report by NINA and the Food and Agriculture Organization of the United Nations, “Crossbreeding a farm with wild salmon can result in reduced lifespan success, decreased life expectancy. individual fitness and a decrease in production over at least two generations ”.

Some researchers, out of caution, have called for making all farmed salmon sexually sterile – a way to restrict this gene flow.

The escapees also bring disease with them. Although more problematic in the tight growing conditions of farmed salmon pens, pathogens such as sea lice have been shown to infect wild salmon populations in Scotland, Canada and Norway, while viruses have been shown to infect wild salmon populations in Scotland, Canada and Norway. salmon have been found in escaped salmon in Norway. It is believed that infected escapees could trigger epidemics in the wild.

The problem of escaped farmed salmon is not new, says Chris Harrod, a fish ecologist at the University of Antofagasta in Chile, which itself benefits from a strong farmed salmon industry. But more work is needed to understand the extent to which escapee genes influence wild populations, especially when farmed and wild fish interbreed and create hybrid offspring.

Fully understanding these impacts is crucial, scientists say, as the genetics of non-wild fish can alter the wild gene pool at a remarkable rate – sometimes in as little as a generation. The new traits that would emerge precisely in the midst of this gene soup are largely unknown and would be difficult to predict, and yet the evidence suggests that hybrid fish are just as likely to survive – and continue to diversify the gene pool – as they are. their wild counterparts. “When they hybridize with wild fish, their offspring can show survival rates similar to those of wild fish,” Harrod said.

Karlsson’s study suggests that some wild populations are more susceptible to intruders than others, but Harrod warns of another issue with escapees that aquaculturists should consider: Once they leave the farm, they compete directly with native fish for resources.

“Escaped fish still need to eat,” Harrod explains, “so even if they don’t reproduce, they occupy the habitat and food needed by native fish. “


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Jeanetta J. Stewart

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