Insecticide-Resistant Sea Lice Spread to Wild Fish

The Maritime Executive –

A new study confirms the role of the aquaculture industry in the spread of resistant salmon lice in Norway.

Until a few years ago, chemical delousing was the most important tool for fighting sea lice in Norwegian salmon farming operations. But after a while, most of the drugs became less effective, because changes in the genes of the sea lice made them resistant. As a result, chemical treatments no longer work as well.

Instead, the continued use of chemicals has led to natural selection that favours sea lice that have the mutation that makes them resistant. These lice multiply more effectively, and researchers have now found a greater number of resistant lice and fewer sensitive ones. It turns out the resistant sea lice are also spreading to wild salmon.

A group of researchers at NTNU in Ålesund, the University of Bergen (UIB), the Norwegian Institute of Marine Research, the Norwegian Institute for Nature Research (NINA) and PatoGen AS have used genetic markers to investigate how the aquaculture industry has affected sea lice in Norwegian fjords.

The same group previously looked at the genetic marker for resistance towards the substance organophosphate used against sea lice. Their new study, published in the scientific journal Aquaculture Environment Interactions, looked at the genetic marker for resistance to pyrethroids.

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