Juvenile Salmon Succumb to Sea Lice

It only takes a few sea lice to kill juvenile pink and chum salmon, and most louse-infested fish die. Salmon that acquired lice in the wild east of Vancouver Island, British Columbia were contained and monitored for over a month, as were uninfested salmon caught at the same time.

Survival rates of fish with lice were considerably lower than for louse-free fish kept under the same conditions after capture.

In one trial, 98% of pink and 88% of chum salmon infested with a motile-stage sea louse died. The few fish with motile lice that survived never hosted more than one louse. Chalimus-stage lice were nearly as deadly. Mortality among uninfested fish in the same trial was close to zero.

Death rates climbed higher for fish hosting more lice. The results indicate that pink and chum salmon native to BC cannot tolerate as many lice as can Atlantic salmon.

Pink salmon often succumbed just after the sea lice they carried reached the motile stage. Chum salmon survived a week or longer with motile lice attached. Over the course of the trials in the Broughton Archipelago, infestation rates dropped as more than half the lice that fish had when first caught disappeared.