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Objective: Chicken gut meal (CGM) is reasonably priced and rich in nutrients and can become a new source of protein in the diets of major aquatic products, such as fish and shrimp. Methods: An 8‐week feeding trial was conducted to comprehensively investigate the beneficial effects of CGM on juvenile Fat Greenling Hexagrammos otakii. Juveniles (1.58 ± 0.06 g [mean ± SE]) were fed with different levels of CGM in replacement of fish meal (FM) in the basal diet: 0% (CGM0), 25% (CGM25), 50% (CGM50), 75% (CGM75), and 100% (CGM100) replacement, representing a dietary CGM level of up to 40 g/kg. Result: The results showed that the percent weight gain; specific growth rate; feeding rate; feed conversion ratio; hepatosomatic index; and apparent digestibility coefficients of dry matter, protein, and lipid were significantly improved among the experimental groups. Moreover, the activities of superoxide dismutase and catalase were significantly increased in the CGM25 and CGM50 groups, respectively. The activities of acid phosphatase and alkaline phosphatase were significantly decreased in the CGM75 and CGM100 groups. Triglycerides and total cholesterol were significantly increased in the CGM50 and CGM75 groups, respectively. Fish in the CGM100 and CGM75 groups had significantly higher activities of aspartate aminotransferase and alanine aminotransferase than the control. Moreover, the relative expression levels of the fatty acid synthase and acetyl‐coenzyme A carboxylase alpha genes were significantly increased in the CGM75 and CGM100 groups, while the gene expression levels of hormone‐sensitive lipase and peroxisome proliferator‐activated receptor alpha were significantly decreased. Conclusion: In summary, the optimal replacement level of FM with CGM was shown by curve equation analysis to be 61.30%, and their dosages were 24.52 and 15.48 g/kg, respectively. Impact statementChicken gut meal, a major terrestrial animal protein source that is rich in high levels of proteins and lipids, can be used as a good substitute for fish meal in fish diets. The price of chicken gut meal is much lower than fish meal, reducing costs. Also, the reduction of fish meal use can restore the diversity and stability of marine fish stocks. Therefore, the use of chicken meal is important for people's health and well‐being as well as the sustainable development of marine fisheries. [ABSTRACT FROM AUTHOR]

Fat greenling (Hexagrammos otakii) is a kind of economic fish that is widely consumed by human, and its intensive farming technology is making important progress. However, high-density farming may cause the occurrence of diseases in H. otakii. Cinnamaldehyde (CNE) is a new feed additive for aquatic animals and has a positive effect on disease resistance. In the study, dietary CNE was evaluated on the growth performance, digestion, immune response, and lipid metabolism of juvenile H. otakii (6.21 ± 0.19 g). Six experimental diets were formulated containing CNE at levels of 0, 200, 400, 600, 800, and 1000 mg/kg for 8 weeks. The percent weight gain (PWG), specific growth rate (SGR), survival (SR), and feeding rate (FR) were significantly increased by including CNE in fish diets regardless of the inclusion level (P < 0.05). The feed conversion ratio (FCR) was significantly decreased among the groups fed CNE supplemented diets (P < 0.05). A significant decrease in hepatosomatic index (HSI) was observed in fish fed 400 mg/kg-1000 mg/kg CNE compared to the control diet (P < 0.05). Fish-fed diets containing 400 mg/kg and 600 mg/kg CNE had a higher level of crude protein in muscles than the control diet (P < 0.05). Moreover, the activities of lipase (LPS) and pepsin (PEP) in the intestinal were markedly increased in juvenile H. otakii-fed dietary CNE (P < 0.05). Apparent digestibility coefficient (ADC) of dry matter, protein, and lipid was significantly increased with CNE supplement (P < 0.05). The activities of catalase (CAT) and acid phosphatase (ACP) in the liver were markedly enhanced by including CNE in juvenile H. otakii diets compared with the control (P < 0.05). The activities of superoxide dismutase (SOD) and alkaline phosphatase (AKP) in the liver were markedly enhanced in juvenile H. otakii treated with CNE supplements 400 mg/kg-1000 mg/kg (P < 0.05). Additionally, the levels of total protein (TP) in the serum were markedly increased by including CNE in juvenile H. otakii diets compared with the control (P < 0.05). In the CNE200, CNE400, and CNE600 groups, albumin (ALB) levels in the serum were markedly higher compared with that in the control (P < 0.05). In the CNE200 and CNE400 groups, the levels of immunoglobulin G (IgG) in the serum were significantly increased compared with that the control group (P < 0.05). The juvenile H. otakii-fed dietary CNE had lower triglycerides (TG) and total cholesterol (TCHO) levels in the serum than fish-fed CNE-free diets (P < 0.05). The gene expression of peroxisome proliferator-activated receptor alpha (PPAR-α), hormone-sensitive lipase (HSL), and carnitine O-palmitoyltransferase 1 (CPT1) in the liver was significantly increased by including CNE in fish diets regardless of the inclusion level (P < 0.05). However, fatty acid synthase (FAS), peroxisome proliferator-activated receptor gamma (PPAR-γ), and acetyl-CoA carboxylase alpha (ACCα) in the liver were markedly decreased with CNE supplements 400 mg/kg-1000 mg/kg (P < 0.05). The glucose-6-phosphate1-dehydrogenase (G6PD) gene expression levels in the liver were markedly decreased compared with the control (P < 0.05). The optimal supplementation level of CNE was shown by curve equation analysis to be 590.90 mg/kg. [ABSTRACT FROM AUTHOR]