2. Combating salmon lice with wrasse fish: The spread of disease in aquaculture poses a serious threat not only to farmed fish, but also to wild fisheries. Although one such disease, salmon lice, occurs naturally in the wild, salmon lice has been intensified by aquaculture because of its high concentrations and varieties of species – in some areas of Norway, for example, wild salmon and sea trout had 3-5 times more lice than what is considered to be a “fatal dose.” Furthermore, the lice can be transmitted from fish to fish or across large distances via currents, making the disease very difficult to contain. If aquaculture contributes to the incidence of a potentially fatal disease in wild habitats, then it may contribute to the collapse of global wild fisheries. For these reasons, scientists from Stirling University in Scotland are studying the effect of wrasse, a family of fish that cleans other fish of parasites and has been shown to help control lice in farmed salmon. If wrasse can effectively control the incidence of salmon lice, fish farms can reduce their use of medicines and other inputs, and limit their environmental impact.
Using wrasse to reduce salmon lice in action: In September 2011 Scotland’s two largest salmon-farming operations announced a joint study with Stirling University in Scotland to determine the best species of wrasse to combat salmon lice. The companies are each investing nearly $700,000 to develop and grow enough wrasse to deploy in Atlantic salmon farms throughout Scotland.