Selective breeding can produce salmon resistant to sea lice, according to a new study.

Sea lice (Lepeophtheirus salmonis) are recognised as the most serious threat to the welfare of farmed Atlantic salmon and the sustainability of fish farming across the world.

Chemical treatment is the current mainstay of controlling infection, but growing drug resistance among sea lice means an alternative is urgently required.

Now scientists at Glasgow University have developed a simple protocol to breed fish that are resistant to sea lice and have produced a mathematical model to predict the response to selection.

The results indicate that fish respond quickly to selection and resistant fish populations will require substantially fewer treatments to control lice.

In some instances as few as 10 generations may produce fish that naturally control infection and seldom require treatment.

Professor Michael Stear, Professor of Immunogenetics in the university’s Institute of Biodiversity Animal Health and Comparative Medicine, said: “Sea lice infection is a major threat to the health of farmed salmon and to the fish farming economy. Our research has produced a practical tool for quantifying resistance to sea lice and shown that selection could substantially reduce the need for drug treatments.

“Selective breeding for sea lice resistance should reduce the impact of sea lice on fish health and thus greatly improve the sustainability of Atlantic salmon production.”

The sea louse can cause skin lesions, osmotic imbalance and increased susceptibility to bacterial and viral infections through suppression of the host immune system.

The study is published in the Royal Society journal Interface.