Can helper species combat sea lice at salmon farms?
Of the roughly 25,000 fish swimming in each of four circular net pens moored off the coast of New Brunswick, Canada, perhaps the most important ones contained therein aren’t even salmon. For every 100 salmon being fattened to market size for restaurants and supermarkets internationally, there are about four or five cunners, a smaller fish that’s been sent in to do a simple job: Feast on sea lice, the finfish aquaculture industry’s most persistent pest. Think of them as ladybugs controlling aphids in a garden.
Sea lice (Lepeophtheirus salmonis) have caused millions of dollars in losses for salmon farms worldwide — as well as bad publicity for one of Canada’s top supermarket chains. One way to get rid of them is a pesticide. Slice (emamectin benzoate) and Salmosan are two common and effective ones on the market, but aquaculture industry critics oppose the use of such substances, fearing dire consequences for other species, like lobsters, that live near the farm sites.
There is, however, an alternative measure under development that doesn’t depend on chemicals and the early results are encouraging. Projects in Norway and Canada, at both the university and corporate levels, are turning to helper fish like the cunner (aka connor or bergall; Tautogolabrus adspersus) and wrasse to remove the lice that enter salmon farms; scientists at the University of Maine in Orono believe mussel rafts placed on the periphery of the finfish farms can also help, as larval lice have been found in mussel bellies and digestive tracts.