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Protein is an essential nutrient that supports fish growth, and the inadequacy in formulating their diets with an optimum protein level can deteriorate their growth performance. The protein requirement in granulated microdiets was estimated for rockfish (Sebastes schlegeli) larvae. Five granulated microdiets (CP42, CP46, CP50, CP54, and CP58) containing 42% to 58% crude protein levels with a 4% increment at a constant gross energy level (18.4 kJ/g diets) were prepared. The formulated microdiets were also compared with imported microdiets, Inve (IV) and love larva (LL) from Belgium and Japan, respectively, and a locally marketed feed (crumble). At the cessation of the study, the survival of larval fish was not different ( P > 0.05 ), but the weight gain (%) of fish fed the CP54, IV, and LL diets was significantly ( P < 0.0001 ) higher than that of larval fish fed the CP58, CP50, CP46, and CP42 diets. The crumble diet achieved the poorest weight gain of larval fish. Furthermore, the total length of rockfish larvae fed the IV and LL diets was significantly ( P < 0.0001 ) longer than that of the fish fed all other diets. The chemical composition of the fish’s whole body, except for ash content, was not influenced by the experimental diets. The experimental diets affected essential amino acid profiles, such as histidine, leucine, and threonine, and nonessential amino acid profiles, such as alanine, glutamic acid, and proline of the whole body of larval fish. Conclusively, based on the broken line analysis of weight gain of larval rockfish, protein requirement in granulated microdiets was estimated to be 54.0%.

Feed additives are essential in improving the growth and immunity of eels, which are often affected by nutritional and disease challenges. This study evaluated the effects of two dietary synbiotics in Japanese eel, Anguilla japonica: Bacillus subtilis with mannooligosaccharide (MOS) and Enterococcus faecium with fructooligosaccharide (FOS). Six diets, including a basal diet (CON), a 4 g kg− 1 oxytetracycline (OTC), and four synbiotic diets - B.subtilis at 1 × 106 and 107 CFU g− 1 plus 5 g kg− 1 MOS (BS6MO and BS7MO) and E. faecium at 1 × 106 and 107 CFU g− 1 plus 5 g kg− 1 FOS (EF6FO and EF7FO) - were prepared and fed to triplicate groups of 20 fish averaging 6.00 ± 0.07g (mean ± SD) for eight weeks. Weight gain (WG) and specific growth rate (SGR), and feed efficiency (FE) of fish fed B. subtilis plus MOS (BSMOS) diets were significantly higher than those of fish fed CON and OTC diets (p E. faecium plus FOS (EFFOS) diets. Best protein efficiency was achieved in fish fed the synbiotics diets (p Vibrio anguillarum. Since synbiotics are dose dependent, the synergetic efficiency of EFFOS is better at 107 CFU g− 1. These results suggest that BS7MO may be more effective as a synbiotic in Japanese eel diet than EFFOS diets. Our results showed that synbiotic diets could improve growth and immunity and be a sustainable alternative to antibiotics.

An 8-week feeding trial was conducted to evaluate the effects of dietary γ-aminobutyric acid (GABA) on growth performance, immune response, and disease resistance for juvenile whiteleg shrimp, Litopenaeus vannamei. Five isonitrogenous diets were formulated by supplementing 0 (CON), 50 (GABA50), 100 (GABA100), and 300 (GABA300) mg of GABA and 4 g of oxytetracycline (OTC) per kilogram of diet. A total of 225 juvenile whiteleg shrimp with an initial weight of 2.97 ± 0.06 g were randomly distributed and reared in 15 aquaria as triplicates. After 8 weeks of the feeding trial, weight gain, specific growth rate, feed efficiency, and protein efficiency ratio of shrimp fed GABA100 were significantly higher than those of shrimp fed CON, GABA50, and GABA300 diets ( P < 0.05 ). However, there were no significant differences among shrimp fed CON, GABA50, GABA300, and OTC diets ( P > 0.05 ). After nine days of challenge test with Vibrio alginolyticus, the average cumulative survival rate of shrimp fed GABA50, GABA100, and OTC was significantly higher than that of shrimp fed GABA300 and CON diets ( P < 0.05 ). These results may suggest that 100 mg dietary GABA supplementation (including endogenous GABA, 175.6 mg/kg diet) per kilogram of diet could be the optimum dietary level to replace antibiotics and improve growth performance and disease resistance in whiteleg shrimp L. vannamei.