An 8-week feeding trial was conducted to assess the effects of different dietary lipid levels on the growth performance, feed utilization, and body composition of juvenile kelp grouper Epinephelus moara. Six diets with varying lipid levels of 2.82%, 5.30%, 7.83%, 11.76%, 14.19%, and 16.32% (designated as CL1 to CL6) were carefully formulated. A cohort of 324 juvenile fish (initial body weight of 5.87 ± 0.09 g fish−1) were randomly divided into six groups with three replicates in each group. The results showed that weight gain (WG) significantly improved as the dietary lipid level increased to 7.83%, followed by a decline with further increases. Fish fed the diet with 7.83% lipids also exhibited the highest feed efficiency (FE) and protein efficiency ratio. Although daily nitrogen intake and daily energy intake varied, no significant differences in nitrogen retention and energy retention were detected among the groups. With the increase in dietary lipid levels, daily lipid intake and daily lipid gain significantly increased, but lipid retention showed a consistent decline. Additionally, the viscerosomatic index and intraperitoneal fat ratio and the lipid content of the whole body, dorsal muscle, and liver increased significantly with increasing dietary lipid levels. The hepatic glycogen content inversely decreased with the elevation in dietary lipid levels. The lowest total cholesterol content in the serum was detected in the 16.32% dietary lipid treatment. According to the second-order polynomial regression analysis of WG and FE, a dietary lipid level of 6.56–9.31% was optimal for the growth performance and feed efficiency of juvenile kelp grouper.

A dietary strategy was conducted with graded crude protein (CP) levels (various from 27.08% to 58.10%) in six semi-purified diets to investigate the appropriate dietary CP supplement for juvenile spotted knifejaw (Oplegnathus punctatus). Experimental diets were respectively offered to the juvenile fish with three replicates (18 individuals each replicate, 19.91 g fish-1) for 8-week. After the feeding trial, the weight gain (WG) was improved by increment of dietary CP levels, but deteriorated slightly when dietary CP over 45.87%. The daily feed intake (DFI) elevated as dietary CP decreasing. Besides, the lowest protein efficiency ratio (PER) and feed efficiency (FE) were observed in 27.08% CP treatment. However, the PER and energy retention (ER) were not significantly different among 32.97%, 39.71% and 45.87% CP groups. In the current study, fish fed diet with 58.10% CP obtained slightly lower PER and nitrogen retention (NR), but relatively higher lipid retention (LR) value compared to those fed a diet with 45.87% CP. And the daily nitrogen intake (DNI) in the fish fed on the low CP levels (27.08 to 39.71%) were significantly lower than that in 45.87% CP treatment. The various dietary treatments did not differ in the visceral index (VSI), hepatosomatic index (HSI) and serum glucose, but fish in the lowest CP group had a decreased intraperitoneal fat ratio (IPF). The protein content in the whole body and dorsal muscle of the fish significantly elevated with dietary protein increasing. The aspartate transaminase (AST) in serum increased with increasing dietary CP from 27.08%-52.65 and then decreased. The regression analysis in second order polynomial and two slope broken-line mode based on NR and WG indicated that the optimal protein supplement for juvenile O. punctatus is 42.92%-46.44%. The present study also indicated that O. punctatus had poor ability to utilization dietary carbohydrate.

An 8-week feeding trial was carried out with various lipid level (2.30 %, 6.31 %, 8.98 %, 12.93 %, 16.08 %, and 18.99 %) diets to investigate the effects on growth performance, body composition, and feed utilization of juvenile spotted knifejaw Oplegnathus punctatus. After the feeding experiment, the weight gain (WG) and specific growth rate (SGR) significantly elevated with raising the dietary lipid level to 12.93 %, and then decreased when dietary lipid further increased (p < 0.05). The tendencies of feed efficiency (FE), protein efficiency ratio (PER), nitrogen retention (NR), and energy retention (ER) were consistent with the growth performance (p < 0.05). The lipid retention (LR) significantly decreased with dietary lipid increasing (p < 0.05). The fish consuming 2.30 % and 6.31 % lipid diets had significantly elevated hepatosomatic index (HSI) (p < 0.05). The intraperitoneal fat ratio (IPF) increased with the increase of dietary lipid levels (p < 0.05). The elevation of dietary lipid levels significantly increased the lipid concentrations in the whole body, dorsal muscle, and liver (p < 0.05). The highest liver glycogen deposition was found in the 2.30 % dietary lipid treatment (p < 0.05). The fish fed the diets added with 12.93 % lipid diet had the highest serum protein concentration (p < 0.05). The lowest total cholesterol (TC) content in the serum was detected in 2.30 % dietary lipid treatment (p < 0.05). The fish fed diets with 2.30 % or 18.99 % lipid obtained elevated serum AST and ALT activities (p < 0.05). The regression analysis in second order polynomial and two slope broken-line mode based on SGR and FE indicated that diet containing 10.46–12.83 % lipids was optimal for juvenile O. punctatus to obtain best growth performance and feed efficiency.

Dietary protein requirement of juvenile kelp grouper Epinephelus moara was investigated through a feeding trial. Experimental diets with graded crude protein (CP) levels (33.01%, 38.54%, 45.21%, 50.71%, 56.10% and 63.09% of dry matter respectively) were formulated. Six triplicate groups of fish (20 individuals per replicate with initial mean weight 6.00 g) were fed with each diet for 8 weeks. Best growth performance of fish was detected in 56.10% CP diet. The specific growth rate (SGR) significantly elevated with increasing dietary CP level to 50.71%, but there was no significant difference thereafter (p < .05). The feed conversion ratio (FCR) decreased significantly with dietary CP levels from 33.01% to 56.10% (p < .05). Glucose (GLU) and total protein (TP) concentrations in plasma had an increasing trend with dietary protein increasing. In the 33.01% CP group, plasma triglyceride (TG) content was significantly higher (1.67 mmol/L) than that in other dietary treatments (0.65-1.14 mmol/L). The lowest alanine transaminase (ALT) activity was observed in the 56.10% CP group (163.16 U/L). Crude lipid content in the muscle and liver was significantly elevated with increasing dietary protein levels (p < .05). The glycogen content in the liver decreased significantly as CP levels increased (p < .05). The fish fed diet with higher CP level (56.10% and 63.09%) had significantly higher energy retention (ER) and lipid retention (LR) than other treatments. Based on the broken-line regression analysis of SGR and FCR, the optimal dietary protein requirement for juvenile kelp grouper is 54.61%-56.22%.

This experiment was carried out to investigate the optimal dietary protein levels for juvenile Scylla paramamosain. Six isoenergtic and isolipidic semi-purified diets were formulated with graded protein levels, and the final protein concentrations were 32.69%, 38.54%, 42.92%, 49.89%, 52.09% and 60.07%, respectively. Each diet was offered to triplicate groups of 28 mud crabs (initial weight 0.04 ± 0.001 g, carapace length 3.3 ± 0.05 mm) for 8 weeks. The results showed that the mud crabs fed diets with 32.69% and 60.07% protein had significantly lower survival than those in other treatments (p < .05). The juvenile mud crab consuming 42.92%, 49.89% and 52.09% dietary protein obtained significantly higher weight gain (WG) and specific growth rate (SGR) than other groups (p < .05). Crude protein content in whole body significantly increased with increasing dietary protein level (p < .05). Crabs fed diet with 49.89% had the lowest hepatic aspartate aminotransferase (AST) activity (p < .05). A relatively higher of hepatic alkaline phosphatase (AKP) activity was observed in groups with 42.92% and 49.89% protein diet (p < .05). The hepatic superoxide dismutase (SOD) activity significantly increased with dietary protein level increasing to 49.89% and leveled off thereafter (p < .05). The EcR mRNA expression level in the eyestalk slightly decreased with increasing protein level to 42.92%, and it then obviously up-regulated with dietary protein content further increasing to 52.09% (p > .05). According to the polynomial regression analysis, 47.06% dietary protein was required for juvenile S. paramamosain to obtain maximum growth rate.