The production of farmed salmon in open net-cages depends on the use of many chemicals—including chemicals to combat sea lice with orally administered pesticides and copper-based antifouling paints applied to salmon cages to prevent the growth of marine organisms.
While regulations are in place to limit consumer exposure where risks to humans have been established, the introduction of chemicals to the environment can pose risks to the marine food chain of which humans are a part.
Many consumers are not aware of the chemical use that may be behind their food. For example, chemicals that have been used in BC salmon farms include: Ivermectin, emamectin benzoate, oxytetracycline, florfenicol, Romet 30, sulfadimethoxine and ormetoprim, sulfadiazine and trimethoprim, tricaine methanesulfonate, formaldehyde, florfenicol and hydrogen peroxide.1
The information below describes some of the main chemicals used in salmon farming and outlines the environmental or health concerns associated with these compounds.
While wild salmon get their colour naturally from the tiny crustaceans like krill they eat, most farmed salmon feed uses synthetic colourants canthaxanthin and astaxanthin to give farmed salmon flesh a pink hue. Without these colourants, farmed salmon would be an unappealing grayish-white color.
A colour fan (as shown above) is a tool the industry uses to choose the colour of their end product—often preferring the vibrant red that consumers associate with healthy, wild sockeye salmon.
One of the most significant and well-studied impacts of salmon farming on wild salmon is the transfer of sea lice from fish farms to juvenile wild salmon during out-migration. In an attempt to control sea lice levels on salmon farms, emamectin benzoate (EB), marketed as SLICE, is added to the feed of farmed fish.
Emamectin benzoate belongs to a class of chemicals called avermectins, which are axonic poisons affecting nerve cells.2 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.3
SLICE lacks specificity; it puts marine organisms in the vicinity of treated salmon farms at risk. A report commissioned by the World Wildlife Fund’s Salmon Aquaculture Dialogue (SAD) found that sea lice therapeutants (such as SLICE) negatively impact the environment through its effects on non-target wild crustaceans such as shrimp, crabs and prawns, and may remain in the environment from ten days to six months.4
In 2003, 37 million farmed salmon in Canada were treated with SLICE. A steady dependence on SLICE by the BC salmon farming industry has been recorded by the Ministry of Agriculture and Lands.5
Up until June 2009 SLICE was only available to fish farmers through the Emergency Drug Release Program, which allows the use of non-approved drugs when recommended by veterinarians for emergency situations. In June 2009, Health Canada quietly approved the use of this chemical and when CAAR contacted Health Canada requesting approval criteria, CAAR was told that research was conducted by the manufacturer, is proprietary, and is not available to the public.
The previously required withdrawal period of 68 days between the last use of SLICE and harvest of the treated fish has disappeared with the approval.
Overuse or over-reliance on any single compound has been shown to lead to the development of resistance by the target organism. Evidence of resistance to SLICE has been occuring in all salmon farming regions that use the chemical.
Due to the prevalence of bacterial infections in salmon farming operations and the risk of diseases such as infectious salmon anemia (ISA), disinfectant protocols are used as biosecurity measures to limit the transfer of diseases from site to site. ISA has never been an issue in BC, but disinfectants are still heavily used to prevent spread of diseases such as IHN and/or furunculosis.
Protocols call for the use of disinfectants on nets, boats, containers, raingear, boots, diving equipment, platforms and decking. Unlike other chemicals, there are no regulations regarding the use of disinfectants.
The Salmon Aquaculture Dialogue (SAD) Chemical report found there is no information on the amounts of disinfectants used by the salmon aquaculture industry, processing plants or the food industry. Without this information it is impossible to determine the impact of disinfectants.4 The UK is the only jurisdiction that requires reporting on disinfectant use.
Disinfectants often contain surfactants (wetting agents that lower the surface tension of a liquid, allowing easier spreading). “Some surfactants are known endocrine disruptors and are known to affect salmon as well as other marine organisms.” 4 An endocrine disruptor is a synthetic chemical that when absorbed into the body either mimics or blocks hormones and disrupts the body’s normal functions.
Until information on the type and quantity of compounds being used in salmon farming is available, it will be impossible to assess the risk these substances pose to salmon and non-target organisms.
Malachite green is a fungicide used for the treatment of external fungal and parasitic infections on fish eggs, fish and shellfish and was once used in salmon aquaculture. Malachite green is not approved for use in fish intended for human consumption.
“Malachite green and its metabolite leucomalachite green are suspected of being capable of causing gene damage and cancer. Its use as a therapeutant in fish destined for human consumption has been banned and a zero tolerance level for food fish is in place in most countries. Despite the fact that the use of malachite green is banned in salmon farming, several reports identify instances of misuse in aquaculture in the US and internationally.” 4
US and Canadian authorities require that malachite green be at levels below 1.0 ppb (parts per billion) in farmed salmon. In December 2007, the FDA conducted a test of one shipment of Marine Harvest Canada and Creative Salmon fish and found it to be above acceptable levels. On December 27, 2007 the Canadian Food Inspection Agency investigated along with the BC ministry of Agriculture and Lands. On of January 11, 2008 the CFIA cleared the farm to resume harvesting.6
There are no recorded incidents of Canadian farms using malachite green since it was banned. Malachite green was used by the pulp and paper industry, photography industry and as a fabric dye. The prevalence of pulp mills on the BC coast may have led to background levels of malachite still present in the marine environment in coastal BC.
Copper has been measured in sediments near salmon farming sites at concentrations higher than the recommended sediment quality guidelines.
Copper-based antifouling paints are applied to salmon cages and nets to prevent the growth of attached marine organisms on them. The buildup of these organisms would reduce the water flow through the cages, decrease dissolved oxygen, and decrease the durability of the nets.4
The reason for concern is the toxicity of copper (and other metals) in sediments, the amount of the copper that can be taken up into organisms and therefore the potential to produce toxic effects. The Salmon Aquaculture Dialogue Chemical report states “as sediments under fish farms tend to be reducing, have high oxygen demand, and high sulfide from the animal wastes and uneaten feed, these sediments should bind metals to a high degree.” 4
The Scottish Environmental Protection Agency requires annual reporting of use of antifoulant paints from each site and these data are available to the public. British Columbia has no such monitoring or reporting requirements to track the impacts of copper-based antifoulants used by the salmon farming industry.
Closed containment systems may significantly reduce the use of chemicals in salmon aquaculture. Find out more about the closed containment solution.
1Access to Freedom of Information Act. (2005). 2003 and 2004 Finfish Aquaculture Waste Control Regulation (FAWCR), Annual reporting information for Mainstream Canada.
2 Valles, S.M. and P.G. Koehler (1997) Insecticides used in the urban environment: Mode of action. University of Florida Institute of Food and Agricultural Sciences: Gainesville, FL. p. 4.
3 Schering-Plough Animal Health Corporation (2002) Potential environmental impacts of emamectin benzoate, formulated as SLICE for salmonids. Schering-Plough Animal Health Corporation: Union, NJ. p. 36.
4 Burridge, Les, Judith Weis, Felipe Cabello and Jaime Pizarro (March 2008). Chemical Use in Salmon Aquaculture: A Review of Current Practices and Possible Environmental Effects. World Wildlife Federation, Salmon Aquaculture Dialogue.
5 BC Ministry of Agriculture and Lands. Sea lice product usage in British Columbia aquaculture 1996-2003.
6 Canadian Food Inspection Agency. (2006) Malachite Green Questions and Answers.