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.