A 3 × 3 factorial feeding trial was conducted to evaluate the production response of juvenile northern snakehead fish (Channa argus). Nine diets containing 3 protein levels (45%, 48% and 51%) and 3 lipid levels (9%, 12% and 15%) were formulated and fed to triplicate groups of juvenile northern snakehead (15.78 ± 0.09 g/fish) for 8 weeks. The formulated diets were named as P45L9, P45L12, P45L15, P48L9, P48L12, P48L15, P51L9, P51L12 and P51L15 (P-Protein, L-Lipid), respectively. Fish fed diets with the lowest protein and lipid combination (P45L9) had the lowest growth performance. Weight gains (WG) of fish fed the 4 diets P48L12, P48L15, P51L9, and P51L12 were not significantly different (P > 0.05), but significantly higher (P < 0.05) than those of fish fed the other diets. Fish fed diets P48L12 and P48L15 had significantly lower (P < 0.05) feed conversion ratios (FCR) than the rest of the treatments. Protein retentions (PR) among fish fed the diets P45L12, P45L15, P48L12, P48L15, P51L9, and P51L12 were similar and significantly higher (P < 0.05) than those of fish fed the remaining diets. Protein sparing effect was observed in the treatments when fish was fed diets containing 45% or 48% dietary protein levels with dietary lipid increased from 9% to 12%. Fish fed diets with 9% lipid tended to have lower viscerosomatic index (VSI), hepatosomatic index (HSI), and whole-body lipid. Increasing dietary protein level significantly increased (P < 0.05) liver moisture and lipid while dietary lipid level increased liver lipid. Intestinal lipase activity increased significantly (P < 0.05) with increasing dietary lipid and protein levels while intestinal α-amylase and protease activities were not significantly influenced (P > 0.05) by dietary treatments. Based on these results, the diet containing 48% protein with either 12% or 15% lipid is the optimal for supporting growth and feed utilization of juvenile northern snakehead under the current testing conditions.

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Clostridium autoethanogenum protein (CAP) is a single‐cell protein derived from ethanol production and may have potential to become a substitute for fishmeal in aquafeeds. A 70‐day feeding trial was conducted with black sea bream (Acanthopagrus schlegelii) (mean initial weight 6.03 ± 0.09 g) to evaluate partial replacement of fishmeal with CAP in diets. Seven isonitrogenous and isoenergetic diets were formulated with graded levels of CAP (0, 4.85, 9.70, 14.55, 19.40, 38.80 and 58.20%) to replace fishmeal. The inclusion of CAP at all dietary levels tested did not significantly affect the growth performance (p > .05). Fish fed the CAP58.20% diet showed a significantly lower feeding rate, with significantly higher protein efficiency ratio and feed efficiency ratio compared with fish fed the other diets (p < .05). No statistical differences were found in dorsal muscle and whole‐body compositions. Total superoxide dismutase in serum of fish fed CAP58.20% diet was significantly lower compared with that of the control. Malondialdehyde, catalase, total antioxidant capacity and digestive enzyme activities revealed no significant differences among dietary treatments. Phosphorus retention efficiency significantly increased, and phosphorus discharge showed a downward trend with increasing CAP inclusion levels. In conclusion, the results indicated that CAP is a safe and effective alternative protein source, which can replace fishmeal in the diet of black sea bream up to 58.20%, without adverse effects on growth performance, antioxidation and digestive enzyme activity. This study has shown the potential of converting industrial waste into a high protein feed ingredient for aquafeeds.

This study investigated the influence of berberine (BBR) supplementation in normal and high lipid diets on lipid metabolism and accumulation in black sea bream (Acanthopagrus schlegelii). Berberine was supplemented at 50 mg/kg to control (Con, 11.1% crude lipid) and high lipid (HL, 20.2% crude lipid) diets and named as ConB and HLB, respectively. After the 8-week feeding trial, fish body length and specific growth rate were significantly reduced by high lipid diets (P < 0.05). Muscle and whole-body crude lipid contents were significantly influenced by both BBR supplementation and dietary lipid level. Fish fed HLB diet had significantly lower serum triglyceride, low-density lipoprotein cholesterol contents, and alanine aminotransferase activity compared with the HL group. The HL group presented vast lipid accumulation in the liver, and hypertrophied hepatocytes along with large lipid droplets, and translocation of nuclear to the cell periphery. These abnormalities in black sea bream were alleviated in the HLB group. Berberine supplementation in high lipid diet significantly downregulated the hepatic expression levels of accα, srebp-1, 6pgd, g6pd and pparγ, whereas the lpl, hsl, and cpt1a expression levels were significantly upregulated. However, the expression levels of these genes showed opposite trends in muscle (except for pparγ). In conclusion, dietary BBR supplementation in high lipid diet reduced hepatic lipid accumulation by downregulating lipogenesis gene expression and upregulating lipolysis gene expression, and it increased muscle lipid contents with opposite trends of the mechanism observed in the liver.

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This study aimed to investigate the effects of graded butyrate glyceride (BG) supplementation levels in high soybean meal diet on juvenile black sea bream. Three hundred and sixty fish were fed diets containing 199 g/kg fishmeal and 450 g/kg soybean meal, with increasing levels of BG at 0, 2, 4, 6, 8 or 16 g/kg for eight weeks. The growth performance of the fish increased with increasing dietary BG supplementation up to 6 g BG/kg, beyond which growth rate reduced significantly (p < .05). Dietary BG supplementation increased the intestinal protease activity, but had no significant (p > .05) effect on lipase and amylase activities. Fish fed the basal diet exhibited villus shortening with a decrease in the number of goblet cells and a reduction in absorptive and digestive epithelial surface, while fish fed ≥4 g BG/kg diets showed a well‐integrated gut, with large absorptive and digestive epithelial surface. Dietary BG supplementation also improved antioxidative capacity by increasing superoxide dismutase and glutathione peroxidase activities while decreasing malondialdehyde content. The inclusion of BG in high soybean meal diets can improve growth performance, maintain healthy gut morphology and enhance antioxidative capacity of black sea bream.

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