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.