Comparative effects of dietary l-carnitine supplementation on diploid and triploid rainbow trout (Oncorhynchus mykiss)

Abstract

This study compared the effects of dietary l-carnitine and ploidy on growth performances and fatty acid content in rainbow trout (Oncorhynchus mykiss). Fish [initial body weight (BW) = 30 g] reared under high density (50 kg biomass m−3) were hand-fed in triplicate (3 tanks treatment−1, 34 fish tank−1) twice a day, with three nutritionally identical diets containing 15, 200 or 530 mg l-carnitine kg−1 of diet. No significant growth differences were observed over a 56-day grow-out period, during which BWs increased threefold. Growth performances and survival were not significantly affected by either ploidy or dietary l-carnitine content, although daily growth index showed an increasing trend (2.52–2.65% day−1) with increasing dietary l-carnitine. Body l-carnitine content increased significantly with dietary l-carnitine content. Diploid fish had higher plasma ammonia (716–725 μmol L−1) and osmolality (297–303 mOsm) levels than triploid trout (523–649 μmol L−1 and 285–291 mOsm, respectively). l-carnitine, ploidy and their interaction showed to affect significantly the concentration of several fatty acids. Palmitoleic (16:1), oleic (18:1) and erucic (22:1) acids showed lower concentrations, while the eicosadienoic (20:2n-6) and arachidonic (20:4n-6) acids were elevated in liver of triploid fish. Eicosapentaenoic acid (22:5n-3) was significantly higher in fish fed 200 mg than in fish fed 15 mg l-carnitine.