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

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.