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 À1 crude protein) and three lipid levels (50, 100 and 150 g kg À1 crude lipid) were formulated. Fish were randomly allotted to 36 aquaria (1.0 9 0.5 9 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 À1 at the same dietary protein level. Fish fed the diets containing 150 g kg À1 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 À1 lipid. Weight gain and SGR significantly increased with increasing dietary protein from 350 to 450 g kg À1 at the same dietary lipid level, and even a little decline in growth with the further increase in dietary protein to 500 g kg À1 . 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 À1 protein and 50 g kg À1 lipid with a P/E ratio of 29.1 mg protein kJ À1 is optimal for growth and feed utilization of P. ussuriensis fingerlings under the experimental conditions used in the study.

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.

An 8-week feeding trial was conducted to determine the optimum dietary methionine (Met) requirement of juvenile Pseudobagrus ussuriensis with an initial average weight of 0.60 g reared in indoor flow-through and aerated aquaria. Six isonitrogenous (430 g kg À1 protein) and isolipidic (50 g kg À1 lipid) test diets were formulated to contain graded levels of crystalline L-methionine (4.9, 9.0, 11.8, 14.2, 18.1 and 20.8 g kg À1 dry diets, respectively) at a constant dietary cystine level of 2.5 g kg À1 dry diets. Equal amino acid nitrogen was maintained by replacing methionine with nonessential amino acid mixture. Fish were randomly allotted to 18 aquaria (1.0 9 0.5 9 0.8 m) with 50 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. No significant difference was observed in survival of fish (84.67-91.33%). Specific growth rate (SGR), weight gain (WG), feed conversion ratio (FCR), protein productive value (PPV) and protein efficiency ratio (PER) were significantly affected by different dietary methionine levels (P < 0.05). WG, SGR PPV and PER increased, while FCR decreased with increasing dietary methionine level from 4.9 to 11.8 g kg À1 (P < 0.05). However, with further increase from 11.8 to 20.8 g kg À1 , WG, SGR PPV and PER significantly decreased, FCR increased (P < 0.05). The whole body and muscle composition were affected by different dietary methionine levels (P < 0.05). Condition factor (CF) increased with increasing dietary methionine levels up to 11.8 g kg À1 (P < 0.05) and after 11.8 g kg À1 methionine diet, but not significant, declines were observed (P > 0.05). Hepatosomatic index (HSI) of the 4.9, 9.0, 11.8 and 14.2 g kg À1 Met diets was significantly higher than that of fish fed diets 18.1 and 20.8 g kg À1 Met diets (P < 0.05). Viscerosomatic index (VSI) of the 4.9, 9.0 and 11.8 g kg À1 Met diets was significantly higher than that of fish fed diets 14.2, 18.1 and 20.8 g kg À1 Met diets (P < 0.05). Quadratic regression analysis of WG and PER against dietary methionine levels indicated that the optimal dietary methionine requirement for maximum growth and feed utilization of juvenile Pseudobagrus ussuriensis was 14.3 and 14.1 g kg À1 dry diet (35.3 and 34.8 g kg À1 dietary protein), respectively, in the presence of 2.5 g kg À1 dry diets cystine.