Growth, feed conversion and chemical composition of Atlantic salmon ( Salmo salar L.) and Atlantic halibut ( Hippoglossus hippoglossus L.) fed diets supplemented with krill or amphipods

The effects of partial replacement of fish meal (FM) with meal made from northern krill ( Thysanoessa inermis ), Antarctic krill ( Euphausia superba ) or Arctic amphipod ( Themsto libellula ) as protein source in the diets for Atlantic salmon ( Salmo salar L.) and Atlantic halibut ( Hippoglossus hippoglossus L.) on growth, feed conversion, macro‐nutrient utilization, muscle chemical composition and fish welfare were studied. Six experimental diets were prepared using a low‐temperature FM diet as control. The other diets included northern krill where 20, 40 or 60% of the dietary FM protein was replaced with protein from northern krill, and two diets where the FM protein was replaced with protein from Antarctic krill or Arctic amphipod at 40% protein replacement level. All diets were iso‐nitrogenous and iso‐caloric. Atlantic salmon grew from 410 g to approximately 1500 g during the 160 day experiment, and Atlantic halibut grew from 345 g to 500–600 g during the 150 day experiment. Inclusion of krill in the diets enhanced specific growth rate in salmon, especially during the first 100 days ( P  < 0.01), and in a dose–response manner in halibut for over the 150 day feeding period ( P  < 0.05). Feed conversion ratio did not differ between dietary treatments, and no difference was found in dry matter digestibility, protein digestibility and fish muscle composition. Good growth rates, blood parameters within normal ranges and low mortalities in all experimental treatments indicted that fish health was not affected either Atlantic salmon or Atlantic halibut fed the various zooplankton diets.