Growth, feed utilization and body composition of juvenile Manchurian trout,<i>Brachymystax lenok</i>(Pallas) fed different dietary protein and lipid levels

Abstract

A 10-week feeding trial with four dietary protein levels (400, 450, 500 and 550 g kg−1 crude protein) and two dietary lipid levels (80 and 160 g kg−1 crude lipid) was conducted to assess optimum dietary protein and lipid levels for the growth, feed utilization and body composition of juvenile Manchurian trout (initial weight 11.80 ± 0.15 g). Fish were fed twice daily (08:30 and 16:30 h) to apparent satiation. The results showed that fish fed the diet with 500 g kg−1 protein and 80 g kg−1 lipid had the highest growth and feed efficiency. However, fish fed the diet with 450 g kg−1 protein and 160 g kg−1 lipid showed comparable growth to that of the fish fed diet 5 (500/80) and had higher protein efficiency ratio (PER), nitrogen retention (NR) and energy retention (ER) than other groups (P < 0.05). Growth, PER, NR and ER of fish fed the 160 g kg−1 lipid diet was significantly higher (P < 0.05) than that of fish fed the 80 g kg−1 lipid diet at 400 and 450 g kg−1 protein diet, whereas these values showed an opposite trend at 500 and 550 g kg−1 protein diet, and the lowest PER, NR and ER was found by fish fed the 400 g kg−1 protein diet with 80 g kg−1 lipid. Fish fed diets with 400 g kg−1 protein had lower feed intake (FI) than that of other groups. Feed intake of fish fed 80 g kg−1 lipid level was significantly lower than that of fish fed 160 g kg−1 lipid diet at 400 g kg−1 protein (P < 0.05), while no significant differences were observed at 450, 500 and 550 g kg−1 protein-based diets. Contrary to moisture content, lipid content of whole body and muscle increased significantly (P < 0.05) with increasing lipid levels. The results of this study indicated that the diet containing 450 g kg−1 protein and 160 g kg−1 lipid, with a P/E ratio of 23.68 g protein MJ−1 would be suitable for better growth and feed utilization of juvenile Manchurian trout under the experimental conditions and design level used in this study.