Changes in amino acid composition in the tissues of African catfish (Clarias gariepinus) as a consequence of dietary L-carnitine supplements

Abstract

A study was undertaken to examine the effect of different amounts of dietary lysine (13 and 21 g kg−1 diet), lipid (80 and 160 g kg−1 diet) and L-carnitine (0.2 and 1.0 g kg−1 diet) on growth performance, proximate composition and amino acid metabolism of the African catfish (Clarias gariepinus). Juvenile African catfish (23 ± 1.5 g/fish) were stocked into 70-L aquaria (16 aquaria, 28 fish/aquarium) connected to a recirculation system during a maximum period of 74 days. All groups were fed at a level of 24 g kg−0.8 day−1 in an experiment run at pair feeding. Animals receiving 1.0 g carnitine accumulated up to six times more carnitine in their tissues than animals receiving 0.2 g (P < 0.05). Acyl-carnitine and free L-carnitine levels increased in the whole body and in tissues. Dietary L-carnitine supplements increased protein-to-fat ratios in the body, but did not affect growth rate. Protein-to-fat ratios were only affected when the biosynthesis capacity of L-carnitine was restricted due to low lysine levels and when there was a shortage of dietary fat. When lysine was offered at 21 g kg−1 feed, dietary L-carnitine supplements did not affect the amino acid concentrations of body tissues. Dietary L-carnitine supplements raised the concentration of glutamic acid > aspartic acid > glycine > alanine > arginine > serine > threonine in skeletal muscle tissue (P < 0.05). Total amino acid concentration in muscle and liver tissues (dry-matter basis) increased from 506 to 564 and from 138 to 166 mg g−1, respectively, when diets were offered with high L-carnitine, low lysine and low fat levels. These data suggest that dietary L-carnitine supplementation may increase fatty acid oxidation and possibly decrease amino acid combustion for energy.