Total replacement of marine oil by rapeseed oil in plant protein rich diets of juvenile lumpfish (Cyclopterus lumpus): Effects on growth performance, chemical and fatty acid composition

Lumpfish is used to control sea lice in open net-pen farming of Atlantic salmon, but little is known about their nutritional requirements. The aim of this study was to investigate the effects of replacing marine oil (MO) with rapeseed oil (RO), in diets incorporating 50 % plant protein concentrates, on the growth, chemical and fatty acid (FA) composition of juvenile lumpfish. Four extruded diets, nearly iso-lipidic (14-15% DM) and iso-nitrogenous (53-54% DM) were produced with either 10 % MO (fish oil : krill oil constant proportion 2.3 : 1; Control), or the MO replaced with either 25 %, 50 % or 100 % replacement with RO to give the diets identified as RO25, RO50 and RO100, respectively. Triplicate groups of fish (7 +/- 0.18 g) were fed the experimental diets ad libitum during 6 weeks. No significant effects were found on growth parameters, specific growth rate, hepatosomatic index (HSI), visero-somatic index, condition factor (CF), and whole body chemical composition when 50 % of MO was replaced by RO. Monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in whole body, liver and muscles were also not affected by the 50 % replacement of MO. Total substitution of MO with RO significantly reduced the growth performance, and CF, but increased the HSI, and crude lipid in whole body and liver, accompanied by lipid deposition. At the end of the experiment, saturated fatty acids (SFA), PUFA, n-3 FA and eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) in whole body, muscles, and liver decreased (p < 0.05), while MUFA, and total n-6 FA increased (p < 0.05) in fish fed RO100. In conclusion, the results of the present study suggest that dietary inclusion of 50 % RO in diets where the protein content was derived from marine/plant origin (50/50), did not impair the growth of juvenile lumpfish.