How do you remove sea lice from farm-raised salmon? Get other fish to eat them.

Dr. Shannon Balfry, who leads on fish propagation research at the Vancouver Aquarium Marine Science Centre explains, “Salmon farmers are looking for sustainable, ocean-friendly alternatives to chemical treatments to reduce the number of sea lice on their farmed fish.”

Sea lice are not exactly like head lice. While head lice are parasitic insects that spend their entire lives on the human scalp feeding on blood, sea lice are parasitic copepods – tiny crustaceans, like crabs and shrimps, which feed on fish skin and mucus. While sea lice are found naturally on most wild salmon, they can be harmful to the fish in large amounts. They are not harmful to humans.

A sea louse attached to a juvenile pink salmon. Photo: Watershed Watch

A sea louse attached to a juvenile pink salmon. Photo: Watershed Watch

Getting other fish to eat the sea lice is a method being used in Norway and Scotland, and now researchers in the Aquarium’s Fish Lab are testing it out with local Pacific species. Shannon says they’re experimenting with perch species, such as the kelp perch (Brachyistius frenatus), which are considered to be “pickers”.

Kelp perch have been known to eat certain parasites off other fishes, but do they have an appetite for sea lice? As we know by our own eating habits, sometimes not even “pickers” will eat everything that is presented to them. However, Shannon’s preliminary research shows that yes, they do. They quickly ate sea lice attached to glass.

The kelp perch.

Kelp perch are being tested to see if they will eat sea lice attached to salmon.

The researchers’ next step will be to see if the kelp perch will eat sea lice attached to the skin of a live salmon.

The results of this research may lead to new sustainable ways to manage salmon farms by letting kelp perch reduce the number of sea lice that may be passed around farmed salmon and to wild juvenile salmon that are swimming by.

Written by Karen Horak, writer-editor, content and digital experience at the Vancouver Aquarium.

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