Effects on growth and gut health in Atlantic salmon (Salmo salar) fed diets containing the macroalgae Porphyra amplissima

Morphological changes and inflammations in the digestive system of Atlantic salmon (Salmo salar) in aquaculture has been linked to the global trend of increasing use of plant-based ingredients in fish feed. Previous research has shown that adding small amounts of algae to feed may counteract these negative effects and even positively impact growth and welfare of fish kept in aquaculture. This study investigated the effect of including 5% and 10% of the local Norwegian algae Porphyra amplissima to feed given to Atlantic salmon fry (Salmo salar). At an inclusion level of 5%, significant increase in wet weight and condition factor was observed. There were some indications of significant increase in fork length when use of the experimental diets, but insufficient statistical power limited to determine whether it originates from the diet with 5% or 10% inclusion levels. There was no statistically significant differences in specific growth rates (SGR) or histological characteristics of the digestive system, between groups given different diets. The significant positive effects on growth at 5% inclusion level and absence of any negative effects on growth or gut health at inclusion levels up to 10% indicate the exciting potential of using P. amplissima as a feed ingredient for Atlantic salmon (S. salar).