DIETARY CARNITINE SUPPLEMENTS INCREASED LIPID METABOLISM AND DECREASED PROTEIN OXIDATION IN AFRICAN CATFISH (CLARIAS GARIEPINUS) JUVENILES FED HIGH FAT LEVELS

摘要

The main reason for supplementing fish diets with carnitine is to increase utilization of dietary lipids and carbohydrates as energy substrate. Effects of dietary carnitine and fat supplements on lipid metabolism were examined in juvenile African catfish (Clarias gariepinus). Duplicate groups (2 aquaria/treatment, 60 fish/aquarium) were fed one of four isonitrogenous diets (36% crude protein), each containing a fat level of 8.5 or 16% diet and one of the two levels of carnitine (basal and supplemented, i.e. 40 and 600 mg/kg, respectively). At the end of the feeding trial (43 days), tissue samples were collected. In addition, blood samples were taken 2 hours preprandial, and 2, 4 and 6 h postprandial. Final weight (76 g), growth rate (2.5% BM/d), feed conversion rate (0.9 g/g) and hepatosomatic index (2.6%) were not affected by dietary treatment. Plasma carnitine rose from 6.2 to 15.7 and from 7.7 to 16.5 umol/ml (in fish fed low-fat and high-fat diets, respectively) when carnitine was supplementedto diets, indicating that dietary carnitine was absorbed. Plasma glucose and lactate dehydrogenase levels decreased with high-carnitine supplements, and an interaction between carnitine and fat levels occurred. Animals receiving 600 mg/kg accumulated 3-fold more carnitine in their tissues than animals receiving 40 mg carnitine/kg diet carnitine. High-fat diets significantly increased acyl-carnitine levels in liver. Fatty acid compositions were significantly affected by dietary carnitine and fat, and their interaction. In contrast to low-carnitine fish, the levels of PUFAs in high-carnitine fish decreased, mainly 22:6n-3 (4.0 vs. 12.2 mg/g), 20:5n-3 (1.8 vs. 5.7 mg/g) and 18:2n-6 (3.8 vs. 9.3 mg/g), but only at high-fat levels. Carnitine supplementationdecreased circulating ammonia levels 2 hours postprandial, but only in fish fed high-fat diets. Although carnitine had no clear effect on growth performance, this study provides evidence that dietary carnitine effects on energy metabolism may be conditioned by the dietary lipid level.