Sea Lice

BC Salmon Farms and Sea Lice Management

B.C. salmon farming companies are transparent in sharing information and reporting data. Atlantic salmon farmers have committed to posting monthly updates of sea lice monitoring data collected on their farm sites, which can be found online.

Sea lice are a naturally-occurring parasite of marine environment and have evolved to attach to migrating salmon as they travel through the ocean.

There are 12 species of sea lice in B.C.’s coastal waters but Caligus clemensi (or C. clemensi, commonly known as the herring louse) and Lepeophtheirus salmonis (or L. salmonis, commonly known as the salmon louse) are the two most commonly studied species in the B.C. coastal environment.

While juvenile salmon are free of sea lice when they enter into the ocean pens, they are susceptible to sea lice infestations, particularly caused by L. salmonis.

B.C. salmon farmers take proactive and preventative measures to ensure their fish host low levels of sea lice – following a range of best management practices and monitoring programs to manage sea lice abundance and ensure that any potential increases in abundance is mitigated.

Atlantic salmon farm employees are required by regulation to examine their fish every two weeks, at a minimum, for regular sea lice counts during March 1 to June 30, to coincide with Out Migration of wild salmon. If those counts show an average of three motile lice per fish, companies are required to take action to reduce the absolute lice count over subsequent weeks. This means either treating the fish (see “Treatments”) or removing them, if a harvest is planned.

When exceeding the three-motile abundance, numbers and the planned management response must be reported to DFO within 7 days.

During the rest of the year, salmon farmers are required to conduct sea lice counts at least once a month. Again, if the abundance threshold of three motile lice has been exceeded, monitoring must increase to every two weeks, and actions must be taken within 30 days to manage motile lice abundance.

In order to forecast measures or actions that might be needed to ensure that farm-raised salmon are not further contributing to the sea lice number on wild fish, B.C. have established wild salmon sea lice monitoring programs in all farming regions of the provinces – working collaboratively with researchers in academia and the government.

Studies have shown that, in British Columbia regardless of the presence or absence of salmon farms, there is wide variability in sea lice prevalence in coastal locations. Research over the past decade shows lice levels are significantly linked with ocean conditions and variations in wild hosts.

Sea lice prevalence can also be related to environmental conditions, with sea lice thriving in warm (higher-than-average) water temperatures. Pairing high temperatures with high salinity (due to decreased freshwater mountain run off, and decreased levels of precipitation in an area) create an optimal environment for sea lice to flourish.


B.C. salmon farmers employ a number of techniques to manage sea lice on farm-raised salmon. These measures include decreasing the number of cultured fish on farms through harvest, and the use of Emamectin benzoate (SLICE©) and Paramove 50©.

SLICE© has been used in British Columbia since 1999 as an effective tool to control sea lice, and is only authorized for use under the professional guidance of a licensed veterinarian. It is milled directly into the feed and used sparingly to ensure sea lice levels on farm-raised salmon remain low and are not a threat to out-migrating juvenile wild salmon.

Salmon farmers continue to research and implement alternative controls for sea lice such as vaccines and non-medicinal controls – including hydrogen peroxide (H2O2) treatments.

Hydrogen peroxide breaks down quickly in water into water and oxygen and does not accumulate in sediment or have a withdrawal period for treated fish. It is not considered a contaminant by the BC Ministry of Environment and is actually recommended by MOE as an alternative cleaner for boaters to use instead of bleach. It is also listed by third-party certification group, the Aquaculture Stewardship Council, as the only parasiticide treatment with a 0 rating for persistence and toxicity in the environment.

Because hydrogen peroxide, in this case, is used for pest control, it is classified as a pesticide. Federal approval and a permit for its use from the BC Ministry of Environment has been granted to salmon farmers in B.C.

Association between sea lice (Lepeophtheirus salmonis) infestation on Atlantic salmon farms and wild Pacific salmon in Muchalat Inlet, Canada

“Our study found that population-level abundances of sea lice on farmed and wild salmon in Muchalat Inlet were very low. Our analyses suggest that farm-origin sea lice can influence the likelihood of L. salmonis being introduced to sympatric juvenile Chum. However, the levels of sea lice infestation observed on these wild fish did not appear to be influenced by the sea lice abundances recorded on farms. Therefore, continued compliance with the current regulations regarding sea lice control on the farms in BC should be an efficient strategy to avoid outbreaks of this parasite on the valuable wild stocks along their migration routes.” Scientific Reports volume 8, Article number: 4023 (2018) doi:10.1038/s41598-018-22458-8

Stay tuned for the latest on sea lice count in British Columbia. The numbers have decreased over the last 2+ years.


Related Links:

Ottawa funds to energize BC seafood production

Are salmon farms killing off wild salmon?

A common vision to protect wild salmon


Around the web:

Fish Health

Scientific research on sea lice

Scientific Reports

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