Interaction effects of dietary lipid and lysine on growth feed utilization and body composition of juvenile grass carp (Ctenopharyngodon idella)

An 8-week feeding trial was designed to investigate the effects of varying dietary lipid and lysine levels on the growth, feed utilization, and blood characteristics of juvenile grass carp (Ctenopharyngodon idella). Six diets were formulated to contain one of three lysine levels (1.5, 1.7, and 2.0%) and one of two lipid levels (2.4 and 5.4%). Each diet was randomly assigned to triplicate tanks of 30 juvenile fish (initial body weight, 3.00 ± 0.02 g). The results showed that the weight gain, specific growth rate, feed efficiency, protein efficiency ratio, nitrogen retention, and lipid retention were significantly affected by dietary lipid and lysine levels (P < 0.05). However, no significant difference was observed in survival among the treatments (P > 0.05). All growth and feed efficiency indices decreased with an increasing dietary lipid level and significantly improved with lysine supplementation (P < 0.05). The dietary lipid levels significantly influenced the moisture and lipid contents of the whole body and muscle: the lipid content of tissue significantly increased with increasing dietary lipid and was inversely correlated with tissue moisture content (P < 0.05). The hepatosomatic index, intraperitoneal fat index (IPF), and serum cholesterol and triacylglycerol contents were significantly higher in fish that were fed the high-lipid diet (P < 0.05). Fish fed the low-lipid diet showed significantly higher amino acid concentrations compared to those fed the high-lipid diet, and the amino acid content improved with lysine supplementation (P < 0.05). Furthermore, dietary lipid, lysine, and their interaction had significant effects on growth performance, IPF, and tissue lipid content (P < 0.05). The results of the present study suggest a positive effect of dietary lysine supplementation on the growth and feed efficiency, serum lipid metabolism improvement, and reduction of IPF in juvenile grass carp.