Effects of dietary carnitine and lipid on growth and body composition of hybrid striped bass (Morone chrysops ♀ x M-saxatilis ♂)

A study was undertaken to investigate the effects of graded dietary levels and different types of carnitine on hybrid striped bass (Morone chrysops female x M. saxatilis male %) fed different levels of lipid. An incomplete factorial design was utilized in which diets containing lipid at either 5 or 10% were supplemented with L-carnitine at 0, 500, or 1000 mg kg(-1) diet, DL-carnitine at 1000 mg kg(-1) diet, or carnitine chloride to provide 1000 mg carnitine kg(-1) diet. Juvenile hybrid striped bass (3.3 g fish(-1)) were stocked into individual 38-l aquaria connected as a brackish water (6 parts per thousand), recirculating system and fed each diet in triplicate for 9 weeks. Supplementation of the diet with 1000 mg carnitine kg(-1) increased muscle carnitine from 35.5 to 47.7 mu g g(-1) tissue. Carnitine supplementation did not result in increased weight gain regardless of carnitine level or type; however, weight gain showed a significant (p < 0.05) response to dietary lipid with fish fed diets containing 10% lipid growing 34% more than fish fed diets with 5% lipid. The hepatosomatic index also was unaffected by diet, but the intraperitoneal fat (IPF) ratio was significantly elevated (5.1 vs 3.2%) in fish fed diets with 10% lipid compared to those fed diets with 5% lipid. Fish fed diets containing 1000 mg carnitine kg(-1) had increased IPF ratio values at 4.7% compared to 3.9% for fish fed the basal diet. Liver lipid also was responsive to dietary treatment, increasing from 6.7 to 8.8% of wet weight as dietary lipid increased from 5 to 10%. The relative quantities of triglycerides, free fatty acids and phospholipids in muscle and liver were not influenced by carnitine level, carnitine type or dietary lipid level. Supplementation of carnitine does not appear to be beneficial to hybrid striped bass based on either growth performance or body composition.