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.
Cleaner fish are used as a preventive measure on farms to keep lice levels under control. Approximately 60 million cleaner fish are used worldwide each year, and demand is increasing. The two types of cleaner fish used are lumpfish (Cyclopterus lumpus) and ballan wrasse (Labrus bergylta) depending on location and water temperature. Lumpfish tend to be better suited to colder water during fall and winter months, whereas wrasse are happier at warmer temperatures in the summer.
Once the cleaner fish get big enough, they are released into the net pens with the salmon, where they have specially-designed refuges and cleaning stations where they get to work gobbling lice. The use of cleaner fish has been effective, according to a spokesperson from Mowi, the world’s largest farmed salmon producer. The company purchased a cleaner fish production facility last year after struggling to control sea lice levels in 2018 at their farms in Chile and Norway, and plan to increase their use of the fish going forward.
Salmon farms face increasing pressure to clean up their act in multiple ways, making eco-friendly and holistic lice treatments more popular. The use of natural predators is only one way to reduce the number of lice on farms. Other methods include flushers, which act like a salmon car wash by using jets of water to detach lice, laser detectors, and mechanisms that bring salmon to deeper water, away from lice near the surface.
As demand for cleaner fish increases, sourcing and animal welfare have to be considered if salmon aquaculture is to continue to move towards greater sustainability. Many cleaner fish are hatchery-raised, however more than half of ballan wrasse are sourced from the wild, according to a Seafood Watch report, which can be detrimental to the ecosystem. Some salmon farms are beginning to operate their own hatcheries to minimize reliance on the capture of wild fish. It’s not exactly a rosy life for the cleaner fish either- no one wants to eat a lumpfish for dinner, and once the salmon are large enough to be harvested, the cleaner fish are killed as well, but they don’t end up on a plate. Questions over the ethics of raising fish that will be sacrificed after each production cycle have been raised, as well as animal welfare concerns about the high percentage of cleaner fish that die in captivity, although sometimes the fish are turned into fishmeal for other farmed species. Research and development are ongoing, however, if done correctly the use of cleaner fish holds the promise of meeting increasing global demand for salmon while reducing the use of medicines on farms.
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