Experiment examines if perch can clean sea lice from farmed salmon
Two local species of Pacific perch are showing aptitude as “cleaner fish” for salmon aquaculture, which could reduce the need for chemical treatments of sea lice on ocean-based fish farms.
Preliminary trials in 2016 showed that both kelp perch and pile perch clean lice from infested salmon.
But a recent series of trials by Shannon Balfry — research associate at the B.C. Centre for Aquatic Health Sciences — have produced spectacular results.
“Pile perch have been known to pick sea lice off other fish in nature, so we thought we would give it a try and it worked,” she said.
In a recent trial four kelp perch were placed in a tank with 40 salmon infested with 370 sea lice and within 10 days only six lice remained.
“It was pretty incredible,” she said.
Video of the perch interacting with infested salmon clearly shows the more “aggressive” cleaner fish start plucking lice from their tank-mates in less than an hour.
Sea lice attach themselves to salmon with tiny hooks, but the perch seem able to remove them without causing injury, she said.
Larger lab-based trials are planned for 2017 and ocean-based trials are in the works for 2018.
B.C. salmon farmers spend a lot of money and energy monitoring and controlling sea lice that are passed from wild salmon to farmed Atlantic salmon. Conditions on the farms can lead to concentrated outbreaks on salmon, which are treated with emamectin benzoate, sold under the trade name Slice.
Sea lice control is crucial to prevent outbreaks on farms from spreading back to wild fish that may be vulnerable to lice damage.
Lumpfish and wrasse are used with success as cleaner fish on salmon farms in Norway and Scotland where they are deployed by the millions.
“They raise more cleaner fish in Norway than we do salmon,” said Jeremy Dunn, executive director of the B.C. Salmon Farmers Association — one of the local funding partners for the research. “It has become its own industry.”
Salmon farming firm Marine Harvest and the industry-funded seafood sustainability organization Sea Pact are also providing funding to continue the research in 2017. Preliminary trials were supported by Fisheries and Oceans Canada and the Vancouver Aquarium.
“Cleaner fish have the potential to become an ecologically friendly way to control sea lice and it will help our member farms achieve (Aquaculture Stewardship Council) certification,” said Dunn. The BCSFA has pledged that all B.C. salmon farms will be certified by 2020.
Field trials will help the researchers determine how many cleaner fish will be required to control lice in a commercial-scale net-pen and when to deploy them.
“When I went to see how this is done in Norway there are a lot of similarities between the way their fish behave and how our (perch) behave,” said Balfry. “I don’t see any reason not to be optimistic about this approach.”
Because perch bear live young, rather than laying eggs, the process of breeding them commercially should be relatively simple. Research on perch nutrition and breeding is proceeding in parallel with the salmon studies.
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