Growth performance, fast muscle development and chemical composition of juvenile lumpfish ( Cyclopterus lumpus ) fed diets incorporating soy and pea protein concentrates

Lumpfish ( Cyclopterus lumpus ) are widely applied as biological delousers in open net -pen farming of Atlantic salmon. As a species new to farming it is necessary to obtain a comprehensive understanding of the capacity of lumpfish to utilize plant derived feed ingredients. A feeding trial lasting for 54 days was conducted to investigate the effects of replacing fishmeal (FM) with a mix of soy protein concentrate (SPC) and pea protein concentrate (PPC) on growth, body chemical composition, and fast muscle fiber cellularity in juvenile lumpfish. Four iso- nitrogenous and isoenergetic diets (52 % crude protein and 14 % crude lipid) were formulated; a FM based diet was used as control (CTRL), and three experimental diets containing SPC and PPC (equal proportions of 1:1), replacing FM on weight basis at 25 % (PP25) 50 % (PP50) and 75 % (PP75). The fish grew from approximately 6.9 g to an average weight of 40.2 g in 54 days. Fish fed PP50 had significantly higher body weight, length and height compared to the other dietary groups. The whole body crude protein content of fish fed PP50 was sig- nificantly higher compared to the CTRL diet, while crude lipids were lower than those on CTRL and PP25 diets. Ash and dry matter did not differ among groups. Probability density functions showed no differences in fast muscle fiber size distributions amongst feeding groups. A higher percentage of smaller fibers in all feeding groups indicated hyperplasia was the dominant mechanism of muscle growth during the experimental period. These results suggest that a mixture of SPC and PPC can replace up to 50 % of FM in diets for juvenile lumpfish without any adverse effects on growth, chemical composition and fast muscle fiber cellularity.