Salmon farms have been plagued by parasitic sea lice (Lepeophtheirus salmonis) since they were first established in Norway in the 1960s. The small crustaceans attach to salmon skin, fins and gills with tiny jaws and live out their lives feasting on the blood, mucous and tissues of the living fish. The resulting scarring and wounds leave fish more susceptible to disease and death. Sea lice infestations are damaging to the natural environment and despite significant research and funding aimed at finding a solution, in-ocean operations have been unable to eliminate them. The use of cleaner fish to pluck sea lice off of salmon as they swim in their pens is becoming more widespread on farms, providing a promising new solution.
According to the Global Salmon Initiative, approximately 60% of salmon eaten worldwide (more than two million tons) comes from farms, mainly in Norway, Scotland, Chile and Canada. While naturally occurring in the ocean, sea lice at high concentrations can be deadly to salmon and costly for fish farmers. According to the Sea Lice Research Center at the University of Bergen in Norway, sea lice cost farms an estimated $350 million each year. Sea lice infect salmon in the wild as well, however, densely populated salmon farms are the ideal habitat for parasites to proliferate. Infestations don’t affect human health or food safety, but when they occur, lice originating inside the farm can be spread to wild fish outside of the farm.
In recent years, infestations have been intensified by climate change and the resulting increase in sea temperatures, disrupting the balance of the surrounding ecosystem and decreasing production as farms pour resources into fighting the losing louse battle. In the past, medicinal treatments have led to drug-resistance in the parasites, and public pressure as well as an industry push to be more green have shifted focus to more sustainable methods of control. National regulations and independent sustainability certification bodies have set limits on the number of lice allowed on farms, and if these limits are reached, farms must treat or harvest their fish to reduce environmental impact.