Using algae extracts (or whole algae) in feeds to reduce salmon lice infestations

Using a species of algae with known bioactive properties, we will test if it can reduce the infection, survival of all stages of salmon lice (Lepeophtheirus salmonis), and their reproductive hatching success when delivered in feed formulations. Using varying concentrations of this algae in formulated feeds, we will determine the effect on egg string production and hatching success of short-term and long-term use of diets. In the short-term trial, Atlantic salmon (Salmo salar) will be infected with adult females and fed with the formulated feeds over two weeks, after which egg strings will be harvested and incubated to determine treatment efficacy. In the long-term trial, salmon will be infected with varying life cycle stages of lice over three months, and egg strings will be harvested and incubated once adult females have developed. A total of 960 salmon postsmolts of 200 g will be used in the trials. In both trials, lice will not exceed 30 per fish, and all fish will be sedated with metomidate before handling to minimise stress. Minimal distress is expected. Before sampling, fish will be sedated with metomidate and euthanized. Replacement is not possible as live fish must be used in order to produce lice eggstrings and to score welfare. Reduction has been performed to a minimum, while still allowing for enough statistical power. Refinement is achieved through choice of tank size so fish will be swimming at normal densities and constantly on an optimal water current during the experiment, both of which will likely decrease aggression and harmful social interactions.

Our experiment will determine if this algae can be used as an in-feed additive treatment to reduce hatching success of salmon lice, which if successful, could be applied to the industry to reduce salmon lice infestation pressures for both wild and farmed fish in Norway.