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One of the greatest challenges in salmon aquaculture today are little creatures known as sea lice. Sea lice are copepods (small crustaceans), which are classified as such for their oar-like feet (see photo).

Photo 1: Life cycle of one of the sea lice species which attack salmon Lepeophtheirus salmonis1

Copepods are present in virtually every aquatic habitat whether salt or freshwater. The difficultly for salmon aquaculture is that sea lice are parasites which attach themselves to the exterior of host fish (salmon) and feed on the mucus, blood and skin, weakening the salmon and making them susceptible to disease. There are two species which are of concern to salmon farmers: Lepeophtheirus salmonis present in Europe and Canada and Caligus rogercresseyi found in Chile. The gravid adult female sea lice is a voracious eater and therefore especially harmful to salmon farms.
To maintain animal health and reduce the risk of endangering migrating wild salmon, salmon farms are required to adhere to strict regulations for sea lice counts. For example, Norway has a limit of 0.5 adult female sea lice per salmon, but a new regulation sets the limit to 0.2 adult female sea lice per fish in the springtime, to further protect wild salmon smolt migrating from freshwater streams to the ocean. To comply with regulations, salmon farms regularly count sea lice and when sea lice levels exceed trigger levels, salmon farms employ treatments to reduce the number of lice to acceptable numbers. Unfortunately, treatments are costly and can stress the salmon, resulting in mortalities. Another side effect of the treatments is reduced growth of the fish, resulting in lower harvest weights.
There are a number of methods to control sea lice: in-feed treatments, bath treatments and cleaner fish. In-feed treatments with chemical additives have become less effective over the years as sea lice develop resistance to parasiticides. As a result, salmon farms have increasingly relied upon bath treatments with chemicals (such as hydrogen peroxide), heated sea water or fresh water to reduce lice levels. Bath treatments are however especially costly, stressful to the salmon and can lead to incidental mortalities. Therefore, more recently, ‘biological’ methods, such as the use of cleaner fish, have been introduced. Cleaner fish, such as wrasse or lumpfish, are raised alongside the salmon and eat the sea lice off the fish. Because cleaner fish are a natural symbiotic approach, their use is referred to as a ‘biological’ control or solution.   
As sea lice are present in every salmon producing region, the fight against sea lice is global. Warming waters, a result of climate change, are exacerbating the problem. In addition to national regulations, aquaculture certification schemes provide additional assurance that sea lice issues are addressed. The salmon farming industry recognizes that no one company can solve this problem alone and that a global collaborative response is necessary to effectively address this challenge. The Global Salmon Initiative (GSI), a pre-competitive platform of leading salmon farming companies around the world, was created with this type of intention in mind and has developed a set of ‘best practices’ to combat sea lice. GSI also promotes transparency of its member companies. To learn more about GSI and the progress in battling sea lice on a country and GSI member company basis, follow this

[1] Source: Atlantic Canada Fish Farmers Association