Effects of supplemental dietary l-carnitine and ractopamine on the performance of juvenile rainbow trout, Oncorhynchus mykiss

Abstract

This study was carried out to investigate a possible protein-sparing action of l-carnitine and ractopamine in rainbow trout, Oncorhynchus mykiss. An 8-week feeding trial was carried out to evaluate the effects of supplementation of three levels of l-carnitine (0, 1 and 2 g kg−1) and two levels of ractopamine (0 and 10 mg kg−1) on growth performance, fillet fatty acid compositions and blood biochemical parameters in a 3 × 2 factorial experimental design. Ractopamine and 1 g kg−1 carnitine improved the specific growth rate (1.03% and 1.05% day−1), feed conversion ratio (FCR, 1.3 and 1.29), protein efficiency ratio (PER, 1.88 and 1.85) of fish and crude protein (73.5 and 73.8) content of fish fillet. l-carnitine and ractopamine increased the levels of albumin, total protein and globulin in the serum of fish. Apart from eicosapentaenoic acid and docosahexaenoic acid, other fatty acids of fish fillet were increased by ractopamine, while total saturated fatty acids were almost intact. However, the total n-3 poly unsaturated fatty acids were reduced by l-carnitine supplementation (P<0.05). The present study showed that 1 g kg−1l-carnitine and 10 mg kg−1 ractopamine each can improve the performance of rainbow trout and their combination in diet could enhance the protein level and change the fatty acids profile in fillet muscle.