An 8-week growth trial was conducted to evaluate the effects of dietary arginine (Arg) levels on growth, gut morphology, oxidation resistance and immunity of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂) juveniles. Seven isoenergetic (1465 kJ (350 kcal)/100-g DM), isoproteic (53·5 % of DM) and isolipidic (7 % of DM) experimental diets were formulated to contain graded Arg levels ranging from 1·9 to 4·7 % (dry weight) at approximately 0·5 % increments. Each diet was randomly assigned to triplicate groups of 16 juvenile fish (average initial body weight: 11·7 (sd0·1) g) and was administered twice daily (08.00 and 16.00 hours). After the growth trial, all remaining fish were fed their prescribed diets for 2 d and then exposed to 4·5 mg Cu²⁺/l water for 36 h. Results showed that growth performance and feed utilisation of experimental fish were significantly affected by different dietary Arg levels. Weight gain % (WG%) of fish was increased as dietary Arg increased, reaching a peak value at 3·8 % dietary Arg level, and when dietary Arg level increased to 4·7 % WG% was reduced. Fish fed 1·9 and 2·2 % dietary Arg levels had higher daily feed intake compared with fish fed other dietary Arg levels. Feed conversion ratios in fish fed 1·9, 2·2, 2·7 and 4·7 % dietary Arg levels were higher than those in fish fed 3·1, 3·8 and 4·1 % dietary Arg levels. Protein efficiency ratio and protein productive value (PPV) increased with an increase in dietary Arg, up to a peak value at 3·8 % dietary Arg level, above which these parameters declined. On the basis of quadratic regression analysis of weight gain % (WG%) or PPV against dietary Arg levels, the optimal dietary Arg requirement for hybrid grouper was estimated to be 3·65 %. Fish fed 3·8 % dietary Arg had higher whole-body and muscle protein contents compared with fish fed other dietary Arg levels. Fish fed 3·8 and 4·1 % dietary Arg levels had higher levels of mRNA for insulin-like growth factor-I and target of rapamycin in the liver compared with fish fed other dietary Arg levels. Hepatic S6 kinase 1 mRNA expression in fish fed 3·8 % dietary Arg level was higher than that in fish fed any of the other dietary Arg levels. Gut morphology, hepatic antioxidant indices and immune indices in serum and head kidney were significantly influenced by dietary Arg levels. In conclusion, the optimal dietary Arg requirement for hybrid grouper was estimated to be 3·65 %, and suitable dietary Arg supplementations improved gut morphology and oxidation resistance of hybrid grouper.

An 8-week growth trial was conducted to study the effects of different corn starch levels on growth and feed utilization of juvenile hybrid grouper (male Giant Grouper Epinephelus lanceolatus × female Brown-marbled Grouper E. fuscoguttatus). Five isonitrogenous (48% crude protein, dry weight basis) and isolipidic (10% crude lipid, dry weight basis) diets were formulated to contain 0, 7, 14, 21, or 28% corn starch, respectively. Each dietary treatment had three replicates. Groups of 22 hybrid grouper juveniles (average initial weight, 2.74 g/fish) were stocked into small floating cages (120 cm long × 70 cm wide × 50 cm high). Triplicate groups of fish were fed each dietary treatment twice daily (0800 and 1600 hours) to apparent satiation. Water quality was monitored daily. Weight gain (WG) of hybrid grouper displayed no significant differences among all experimental groups. Fish fed 0% corn starch had significantly higher daily protein intake than fish fed 7, 14, 21, and 28% corn starch. The feed conversion ratio (FCR) and daily feed intake (FI) were significantly higher in fish fed diets with 0% corn starch, but FCR and FI were not observed to vary among fish fed any of the other experimental diets. Fish fed 0% corn starch had a lower protein efficiency ratio (PER) than fish fed other experimental diets, and the differences were significant when compared with fish fed 21% or 28% corn starch. Intraperitoneal fat (IPF) ratios did not show significant variations among all experimental treatments. The hepatosomatic index (HSI) of fish fed 0% corn starch were significantly lower than that of fish fed 14, 21, and 28% corn starch. Whole-body moisture, protein, lipid, and ash contents as well as muscle moisture, protein, and lipid contents showed no significant differences among all experimental groups. Hepatic glycogen content increased as dietary corn starch level increased. Fish fed the diet with no corn starch had more protein content in the liver than fish fed 14, 21, or 28% corn starch. Generally, supplementations of 7–28% dietary corn starch could reduce dietary protein input and improve feed utilization of hybrid grouper without negatively affecting their growth.

A 6-week growth trial was conducted to evaluate the influences of dietary valine (Val) levels on growth, protein utilisation, immunity, antioxidant status and gut micromorphology of juvenile hybrid groupers. Seven isoenergetic, isoproteic and isolipidic diets were formulated to contain graded Val levels (1·21, 1·32, 1·45, 1·58, 1·69, 1·82 and 1·94 %, DM basis). Each experimental diet was hand-fed to triplicate groups of twelve hybrid grouper juveniles. Results showed that weight gain percentage (WG%), protein productive value, protein efficiency ratio, and feed efficiency were increased as dietary Val level increased, reaching a peak value at 1·58 % dietary Val. The quadratic regression analysis of WG% against dietary Val levels indicated that the optimum dietary Val requirement for hybrid groupers was estimated to be 1·56 %. Gut micromorphology and expression of growth hormone in pituitary, insulin-like growth factor 1, target of rapamycin and S6 kinase 1 in liver were significantly affected by dietary Val levels. In serum, fish fed 1·58 % dietary Val had higher superoxide dismutase, catalase, lysozyme activities and IgM concentrations than fish fed other dietary Val levels. Fish fed 1·58 % dietary Val had higher expression of NF-E2-related factor 2 in head kidney than fish fed other dietary Val levels. Generally, the optimum dietary Val requirement for maximal growth of hybrid groupers was estimated to be 1·56 % of DM, corresponding to 3·16 % of dietary protein, and dietary Val levels affected growth, protein utilisation, immunity and antioxidant status in hybrid groupers.

This study is aimed at evaluating the effects of dietary protein-to-energy ratios on the growth, immunological response, antioxidative capacity, liver and intestinal histology, and growth-related gene expression of hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂). Eight diets were formulated to form different protein/energy ratios of 84, 88, 90, 93, 95, 96, 99, and 103 mg/kcal (P/E84, P/E88, P/E90, P/E93, P/E95, P/E96, P/E99, and P/E103), respectively. These diets contain different levels of gross energy (GE), ranging from 4.13 to 4.76 kcal g^-1. Seven hundred and twenty healthy fish ( g) were randomly dispersed into 24 rectangular fiberglass tanks with 8 treatments in triplicate groups. The fish fed a P/E ratio of 95 mg/kcal demonstrated the best growth and feed utilization. A significant ( ) increase in percent weight gain (WG%) and specific growth rate (SGR) was seen as the dietary P/E ratio ameliorated from P/E84 to P/E95, followed by a decreased pattern in these parameters. Feed conversion ratio (FCR) and daily feed intake (DFI) were significantly impacted by dietary P/E ratios ( ). Additionally, an optimum P/E ratio improved intestinal morphology. However, low or high P/E ratio diets can cause oxidative stress, impaired liver function, and significantly reduced nonspecific immunity. The expression of target of rapamycin (TOR) and insulin-like growth factor-1 (IGF1) genes in the liver was considerably influenced by dietary protein-to-energy ratios ( ). Based on the statistical analysis of WG% against the dietary P/E ratio, the optimal P/E ratio for the studied species was estimated to be 92.92 mg/kcal.