Dietary lipid level but not L-carnitine affects growth performance of hybrid striped bass (Morone chrysops ♀ X M-saxatilis ♂)

The objectives of this experiment were to determine if dietary lipid levels in excess of previously reported minima would increase performance of hybrid striped bass, and to determine if supplementation of L-carnitine would improve growth and/or body composition when feeding elevated dietary lipid. Therefore, a 2 X 4 factorial design was utilized to test the efficacy of dietary L-carnitine at 0 and 3000 mg/kg diet at each of four lipid levels (5%, 10%, 15% and 20%). Semipurified diets were formulated to contain 40% crude protein and dextrin was substituted for menhaden oil at a rate of 2.25 to 1 to maintain digestible energy at approximately 14.2 kJ/g. Juvenile reciprocal cross hybrid striped bass initially averaging 2.5 g/fish were cultured in a 5 parts per thousand brackish water recirculating system and fed twice daily at a rate approaching apparent satiation. At the end of the 8-week feeding trial, L-carnitine supplementation did not influence weight gain, but dietary lipid level did, with the lowest value (1084% of initial weight) achieved by fish fed 5% lipid and the highest (1343%) by fish fed 15% lipid; fish fed 20% lipid had intermediate weight gain (1215%). Feed efficiency also was influenced by dietary lipid with fish fed the 10% and 20% lipid diets having higher feed efficiency values than those fed the 5% and 15% lipid diets. Body condition indices were only slightly altered by L-carnitine supplementation, but dietary lipid over 10% influenced body condition. Liver composition was altered by dietary lipid level but not L-carnitine supplementation. As dietary lipid level increased, liver lipid increased and liver glycogen decreased dramatically, especially in fish fed the diet with 20% lipid, which had no soluble carbohydrates. Muscle composition was unaltered by any dietary treatment. In conclusion, hybrid striped bass generally did not utilize dextrin as efficiently as lipid, and lipid levels between 10% and 15% of diet provided maximum growth with intermediate lipid deposition. (C) 2000 Elsevier Science B.V. All rights reserved.