Fish farms are unnatural breeding grounds for sea lice due to the high densities of fish in small areas, the net-cages. The significantly higher number of lice in surrounding waters is particularly perilous for wild juvenile salmon heading for the ocean.

Fish farms use chemical treatments to combat the problems of sea lice. SLICE is the commercial name for emamectin benzoate, the preferred chemical for sea lice control in Canada.

To date, SLICE has:

• not been tested for food safety by the Canadian Food Inspection Agency
• not been licensed by the Bureau of Veterinary Drugs (Health Canada)
• not been permitted for use through the Pesticide Control Act

Yet, SLICE is the only chemical used to control sea lice in BC. Salmon farmers are approved to use SLICE through the Emergency Drug Release Program, which allows the use of non-approved drugs when recommended by veterinarians for emergency situations.

SLICE is not used for the occasional emergency. Outbreaks of sea lice are so prevalent in industrial net-pens that the use of SLICE has become standard operating procedure. In 2003, 37 million farmed salmon in Canada were treated with SLICE. ¹ A steady dependence on SLICE by the BC salmon farming industry has been recorded by the Ministry of Agriculture and Lands.²

According to BC regulation, salmon farms must use chemical treatments when a threshold of three motile sea lice per fish is reached. This regulation was developed without consideration of scientific research that shows the high vulnerability of wild juvenile pink and chum salmon to sea lice infection. Because of the tiny size of these wild salmon when they are juveniles, and the proximity of farms to wild salmon migration routes, this regulation has not proven effective in protecting BC’s wild salmon from fatal sea lice infections.

Emamectin benzoate belongs to a class of chemicals called avermectins, which are axonic poisons affecting nerve cells.³ Farmed fish ingest SLICE as a coating on commercial food pellets. Digestion releases the drug to pass through the lining of the fish’s gut and into the fish’s tissues, from where it takes about a week to be eliminated.⁴ Although SLICE contains emamectin benzoate (0.2%), an active ingredient in pesticides, it is classified as a drug because it is fed to the fish rather than applied externally.

Because of its ability to accumulate in sediments, SLICE could become toxic to marine life. In fact, the label of the pesticide ‘Proclaim’, in which emamectin benzoate is the only active ingredient, clearly warns that, “This pesticide is toxic to fish, birds, mammals, and aquatic invertebrates. Do not apply directly to water, or to areas where surface water is present, or to intertidal areas below the mean high water mark. Do not contaminate water when cleaning equipment or disposing of equipment wash water.”⁵

Meanwhile, reports from Chile and Norway indicate that sea lice are showing signs of resistance development to treatments, including emamectin benzoate, likely due to frequent and heavy applications.

Open net-cages perpetuate this chemical dependency. By design, open nets cannot prevent the transfer of parasites between farmed and wild fish.

Closed containment technology could help to address these issues. Learn more about closed system aquaculture.

References
¹Health Canada, Emergency Drug Release Form, Obtained under the Federal Access to Information Act.
² BC Ministry of Agriculture and Lands (2004) Sea lice product usage in British Columbia Aquaculture.
³ Valles, S.M. and P.G. Koehler, Insecticides used in the urban environment: mode of action. 1997, University of Florida Institute of Food and Agricultural Sciences: Gainseville, FL p. 4
⁴ Schering-Plough Animal Health Corporation, Potential environmental impacts of emamectin benzoate, formulated as SLICE for salmonids. 2002, Schering-Plough Animal Health Corporation: Union, NJ p. 36.
⁵ Novartis, Proclaim Insecticide. 1999, Novartis Crop Protection, Inc.: Greensboro, NC p. 7.