Effects of l-lysine supplementation of diets with different protein levels and sources on channel catfish, Ictalurus punctatus (Rafinesque)

Abstract. Semipurified diets containing either 25% or 30% crude protein (CP) from soy isolate (soy) or 30% CP from casein and gelatin (casein) were supplemented with either of two levels of L-lysine HCI (0 or 0·5% of diet) in a 3 × 2 factorial arrangement and fed to fingerling channel catfish, Ictalurus punctatus (Rafinesque), in aquaria for 8 weeks. Factorial analysis of variance indicated a significant ( P < 0·001) positive effect of lysine on weight gain, protein conversion efficiency (PCE) and feed efficiency. Fish fed the soy diet containing 25% CP showed increased weight gain of 24% with lysine supplementation while fish fed soy and casein diets containing 30% CP showed increases of 11 % and 3%, respectively. However, supplementing the 25% CP soy diet with 0–5% L-lysine HCI did not enhance growth performance to the level offish fed the unsupplemented 30% CP soy diet. Significant effects of dietary protein levels and sources on weight gain, PCE, feed efficiency, haematocrit, hepatosomatic index (HSI; % liver weight), intraperitoneal fat (IPF) ratio, dry matter of fillet and whole-body, as well as lipid and protein content of whole-body tissue, were also observed. Fish fed the casein diet containing 30% CP had the greatest weight gain, PCE, feed efficiency, haematocrit and whole-body protein values and lowest IPF ratio and whole-body lipid values compared with those of fish fed the soy diets. Supplemental lysine did not affect body condition indices or proximate composition of whole-body and fillet tissues of fish fed the different protein sources. Therefore, based on this study, dietary protein levels and sources significantly influenced performance characteristics of channel catfish and supplemental lysine was most beneficial at a reduced CP level.