What is a sea louse?
Sea lice are small marine parasites commonly associated with salmon. There are 13 different species of sea lice found on the coast of British Columbia. Although large numbers of sea lice are usually associated with fish farming, sea lice originated from wild fish and, as early as 1940, long before the development of fish farming, there were reports of high numbers of lice causing severe damage/mortality in wild fish. Sea lice are common on adult salmon, and usually don’t cause major physical damage.
Two lice species typically found on farmed salmon are Lepeophtheirus Salmonis(or Leps for short) and Caligus Elongatus.
Caligus Elongatus
Considered not host specific. a parasite living on fish. It feeds on the mucus, skin and blood of the fish. There are approximately 200 known species. Caligus has been found on more than eighty different fish species in most of the world’s oceans. This louse doesn't seem to be as much a problem as Leps.
Lepeophtheirus Salmonis(Leps)
Grows to a length of 5 mm for the males, 10 mm for the females. Each generation takes about six weeks at a temperature between 10 and 12°C (50-54°F). Found on Pacific Salmon, farmed salmon and the three-spine sticklebacks. As sea lice develop from eggs to adults, they shed their exoskeletons in a series of moults. This creates a number of identifiable life stages.
Life-cycle of Sea Lice
Free-swimming larval stages - Nauplius I, nauplius II.
Immature attached stages - Copepodid, chalimus I, II, III and
Motile stages - (Lepeophtheirus) Pre-adult I, Pre-adult
- (Caligus,Lepeophtheirus) Mature adults
Sea lice in the first two stages are called nauplii. Nauplii can neither feed nor attach themselves to fish. In the next, copepodid, stage, the lice can attach themselves to fish (by a frontal filament). They then moult through four chalimus stages during which they are anchored to a host fish. As pre-adults (two stages) and adults (one, final stage), they can move about the host fish. It appears that they are most damaging to the host fish in these final, motile stages.
Yearly changes in population of Leps on high-seas Pacific salmon
http://www.springerlink.com/content/u833251k87778668/Salmon Farmers do monthly lice counts, sampling 20 fish per pen in three pens. A BCSFA database is updated every month. Sampling intensity is increased to twice per month when lice levels reach 3 motile per fish.
The DFO is responsible for wild salmon. The province has jurisdiction over salmon farms. They are working together to monitor and manage sea lice levels. In the fall, levels of sea lice on fish farms tends to increase due to the return of wild stock to spawn. Veterinarians treat these fish to reduce lice levels. Typically, SLICE (EMAMECTIN BENZOATE) is used milled in feed.
SLICE (Emamectin Benzoate) Information Released by the Association of Aquaculture Veterinarians of British Columbia, December 14, 2004
SLICE (emamectin benzoate) is a therapeutant manufactured by Schering- Plough for the control of sea lice in farmed salmon. The product was submitted for approval in both the US and Canada in 1999. Both countries have very strict drug approval processes, and both Health Canada’s Veterinary Drug Directorate (VDD) and the US Food and Drug Administration’s Center for Veterinary Medicine are still reviewing the submission. In the interim the product is being used by veterinary prescription in both countries under strictly controlled situations.
In Canada the review of a new veterinary drug must undergo rigorous scrutiny and fully satisfy all scientific requirements under the Regulations to the Food and Drugs Act.i If a submission is accepted and the product is approved, the manufacturer receives a Notice of Compliance from Health Canada specifying the terms and conditions under which the drug can be sold and used. The drug must bear a Drug Identification Number (DIN) on its label. In Canada, Emergency Drug Releases (EDR’s) may be issued by Health Canada’s Veterinary Drugs Directorate to permit the manufacturer of a new drug to sell a limited quantity of the new drug to a veterinary
practitioner. Adequate evidence is required that the drug poses no known health risk to the animals to be treated or to consumers. The veterinarian must make a detailed submission, and after treatment report to the manufacturer and to the VDD on the results of the use of the new
drug, including efficacy and information respecting any adverse reactions encountered. The report must account for all quantities of the drug received.
For SLICE administered under an EDR, the Veterinary Drugs Directorate set an administrative Maximum Residue Limit (MRL) of 50 ppb (parts per billion) and a withdrawal time of 25 days, i.e., the number of days between harvest and the last day the drug was administered.
SLICE is registered in several countries. In Europe, the UK and Chile there is a 0 day withdrawal time and a tolerance of 100 ppb (allowable level of drug in harvested fish tissue). These numbers are derived from risk assessments based on amounts of fish consumed and knowledge of toxicology testing for emamectin benzoate. In Norway the withdrawal time is 175 degree-days (e.g., 17.5 days at a water temperature of 10 degrees Centigrade).
Emamectin is approved for use in Japan and in the US on vegetable crops. In the US, SLICE is also permitted to be used in food fish in Maine under an INAD (Investigational New Animal Drug) process. This requires a veterinary prescription and is monitored by the US Department of Agriculture (USDA). The drug has a 60-day administrative withdrawal period.
US regulations, based on US Environmental Protection Agency (EPA) assessments, allow for use of emamectin benzoate on leafy vegetables, turnip greens, cottonseed, fruiting vegetables and products such as tomato paste. Tolerance for combined residues of emamectin and its
metabolites range from .02 ppm (20 ppb) to .10 ppm (100 ppb). Regulations also establish tolerances for “indirect or inadvertent combined residues of emamectin” in food animals that may consume these vegetables. These range from .002 ppm (2 ppb) in meat of cattle, goats,
hogs and horses to .02 ppm (20 ppb) in liver tissues of cattle, goats, hogs, horses and sheep.
These tolerances are based on average consumption rates for each product and toxicological assessments of emamectin. “Based on these risk assessments, EPA concludes that there is a reasonable certainty that no harm will result to the general population…from aggregate exposure to emamectin residues. ” In the same regulations, emamectin is classified as a “not likely” human carcinogen.
Preliminary information from the British Columbia Ministry of Agriculture, Food and Fisheries indicates that the amount of product administered to farmed fish in British Columbia in 2003 was approximately 0.08 gm/ tonne of fish produced.vii Not all farm salmon sites were treated and, of those that were, only two sites were treated more than one time during the year.
In Canada, food safety testing is the responsibility of the Canadian Food Inspection Agency (CFIA). CFIA may target their testing or do generic testing for all products used in finfish. When EDR’s are approved, Health Canada notifies the CFIA regionally, and prescribing veterinarians are required to contact CFIA prior to the harvest of any populations treated with SLICE. Regulation in British Columbia also requires each lot of finfish sent to a processing plant to be
accompanied by detailed documentation for all therapeutants used. CFIA has tested approximately 100 samples per year Canada-wide for emamectin benzoate in the last two to three years. A large proportion of these samples were negative for emamectin benzoate, and of those that were positive, all were below Health Canada’s limits. As a result CFIA did not have to take any regulatory action during that timeix. In summary, the use of SLICE in Canada follows the strict regulatory controls established for the use of drugs in food producing animals. Withdrawal times in both Canada and the US are stricter than in countries where the drug has already been approved. In the last two to three years testing of harvested fish shows that there has been no finding of emamectin benzoate residues above limits set by Health Canada.
Lice outbreaks generally happen when wild salmon return to streams for spawning. That is what our year round lice sampling data tells us. Our vet then treats those fish with Slice. Our fish are not infected with lice until the next return of wild stock. For SLICE administered under an EDR, the Veterinary Drugs Directorate set an administrative Maximum Residue Limit (MRL) of 50 ppb (parts per billion) and a withdrawal time of 25 days.
US regulations allow use of emamectin benzoate on leafy vegetables, turnip greens, cottonseed, fruiting vegetables and products such as tomato paste. Tolerance for combined residues of emamectin and its metabolites range from .02 ppm (20 ppb) to .10 ppm (100 ppb).
CFIA has tested approximately 100 samples per year Canada-wide for emamectin benzoate in the last two to three years. A large proportion of these samples were negative for emamectin benzoate, and of those that were positive, all were below Health Canada’s limits.
Use of SLICE in Canada follows the strict regulatory controls established for the use of drugs in food producing animals. Withdrawal times in both Canada and the US are stricter than in countries where the drug has already been approved. In the last two to three years testing of harvested fish shows that there has been no finding of emamectin benzoate residues above limits set by Health Canada.
