Tiny parasite; big problem

“It’s one of those cases where you knew it was when, not if, the problem would arrive, and yet there was little that could be done to solve it until it became a dire situation,” explains Dr. Larry Hammell, Innovation PEI Research Chair and director of the AVC Centre for Aquatic Health Sciences.

Hammell and his team at CAHS have been working for several years to find a solution to the problem of sea lice in farmed salmon. Sea lice are a natural parasite (actually belonging to the crustacean family and not a true louse) that attach to and feed on salmon. They occur naturally in the wild, but are more of a recurring problem in farmed fish.

“In the wild, salmon are always moving,” says Hammell. “They pick up early-stage sea lice, and drop off eggs. A wild Atlantic salmon might have up to 20 sea lice on it without any real problems.”

Sea lice: Photo:  L. HammellSea lice: Photo: L. Hammell

In an aquaculture environment, Hammell explains the salmon can’t escape the sea lice. At the peak of summer, when the water temperature is optimal for sea lice, a new generation can develop every two weeks.

“We have some very effective tools for treating sea lice. The one farmers have used in Atlantic Canada for the last eight or nine years has been very effective. You would have been hard-pressed to find uncontrolled infection during that time. But sea lice, like any parasite, are tricky. They can eventually adapt to these tools.”

Hammell says salmon farms in Chile first reported sea lice developing resistance to this same treatment about two or three years ago. Concerns that sea lice in the Bay of Fundy might develop the same resistance were realized this past summer.

“Resistance developed almost simultaneously in farmed salmon in the Bay of Fundy, Scotland, and Norway — which is a real mystery,” says Hammell. “We know wild salmon from these three areas meet as part of their migration somewhere in the North Atlantic, but farmed salmon don’t migrate. We’re investigating the epidemiology of this resistance.”

Photo:  L. HammellPhoto: L. Hammell

In the meantime, there are other treatments for sea lice, but Hammell says there are regulatory hurdles to clear.

“The product we used in the Maritimes was delivered in salmon feed. There are a couple of other treatments we could consider that go in the cage as a bath using a tarp enclosure. An ideal situation would be to use multiple prevention methods and rotate treatments to not give the sea lice a chance to build up resistance but, until recently, there was not a lot of incentive for drug companies to go through the cost of registering their product in Canada. Our group is helping salmon farms and veterinarians pursue several avenues by evaluating the response to these new treatments in controlled field trials. It is a race to identify the optimal integrated strategy that reduces the impact of lice before next summer brings lice-favourable conditions again.”