Effects of dietary protein and lipid levels on growth, feed utilization and body composition inPseudobagrus ussuriensisfingerlings

Abstract

An 8-week feeding trial was conducted to investigate the optimum dietary protein and lipid levels for growth, feed utilization and body composition of Pseudobagrus ussuriensis fingerlings (initial weight: 3.40 ± 0.01 g). Twelve diets containing four protein levels (350, 400, 450 and 500 g kg−1 crude protein) and three lipid levels (50, 100 and 150 g kg−1 crude lipid) were formulated. Fish were randomly allotted to 36 aquaria (1.0 × 0.5 × 0.8 m) with 25 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. The results showed that weight gain and specific growth rate (SGR) decreased with increasing dietary lipid level from 50 to 150 g kg−1 at the same dietary protein level. Fish fed the diets containing 150 g kg−1 lipid exhibited higher feed conversion ratio (P < 0.05), lower protein efficiency ratio (PER) and nitrogen retention efficiency (NRE) relative to fish fed the diet containing 50 and 100 g kg−1 lipid. Weight gain and SGR significantly increased with increasing dietary protein from 350 to 450 g kg−1 at the same dietary lipid level, and even a little decline in growth with the further increase in dietary protein to 500 g kg−1. Daily feed intake, NRE and PER were significantly affected by both dietary protein and lipid levels (P < 0.05) and tended to decrease with increasing dietary protein and lipid levels. Whole-body protein content increased as protein levels increased and lipid levels decreased. Whole-body lipid and muscle lipid content increased with increasing dietary lipid level, and decreased with increasing dietary protein at each lipid level. There was no significant difference in condition factor and viscerosomatic index among fish fed the diets. Hepatosomatic index was affected by dietary lipid level (P < 0.05), and increased with increasing dietary lipid level at the same protein level. These results suggest that the diet containing 450 g kg−1 protein and 50 g kg−1 lipid with a P/E ratio of 29.1 mg protein kJ−1 is optimal for growth and feed utilization of P. ussuriensis fingerlings under the experimental conditions used in the study.