Effects of supplemental lysine and methionine in low protein diets on weight gain and body composition of young channel catfish Ictalurus punctatus

Two experiments were conducted to evaluate the effects of supplementation with lysine, methionine, or both in low protein but amino acid (AA)-replete diets on weight gain and body composition of channel catfish (mean initial weight: 10-11.9 g/fish) raised under laboratory conditions. In experiment 1, a 2 x 3 factorial arrangement with two feeding rates (approximately 75 and 100% satiation) and three test diets was used. Diets 1 and 2 were formulated to contain 32 and 24% crude protein, respectively. Diet 3 was the same as diet 2 except that 0.4% supplemental lysine was added. Fish were fed once daily for 12 weeks. In experiment 2, a 2 x 4 factorial arrangement with two dietary protein levels (24 or 28%) and four AA supplements was used. Lysine, methionine, or both were supplemented to the basal diets to bring the level of these two essential AAs to 30% above the requirement for channel catfish. Fish were fed once daily to approximate satiation for 12 weeks. In both experiments, five aquaria were used in each dietary treatment. In experiment 1, regardless of feeding rate, fish fed diets containing 24% protein with or without supplemental lysine gained less weight and converted feed less efficiently than fish fed the 32% protein diet. There were no differences in weight gain between fish fed the 24% protein diets with and without supplemental lysine. Feed efficiency of fish fed the 24% protein diet with supplemental lysine was higher than that of fish fed the diet without supplemental lysine. Fillet fat of fish fed diets containing 24% protein with or without supplemental lysine was greater than that of fish fed the 32% protein diet. There were no differences in fillet fat between fish fed the 24% protein diets with and without supplemental lysine. Fillet protein was not affected by diet or feeding rate. In experiment 2, regardless of dietary protein concentration, no significant differences were observed in weight gain, feed consumption, feed efficiency, or fillet composition among fish fed diets with or without supplemental AAs. Results from this study indicate that supplementation with lysine and/or methionine in low protein but AA-replete diets is not beneficial for channel catfish. (C) 1998 Elsevier Science B.V. All rights reserved.