Mitigation of cold stress in Nile tilapia (Oreochromis niloticus) through dietary lipids supplementation: a preliminary network meta-analysis

There is a growing body of evidence suggesting that water temperature can significantly impact the dietary fatty acid requirements of Nile tilapia (Oreochromis niloticus). Therefore, this study assessed the effectiveness of different dietary lipid sources on the growth performance of Nile tilapia reared at suboptimal temperatures. A network meta-analysis was performed, including searches of PubMed and Scopus from inception to January 2022, for trials that evaluated the effects of lipid sources on cold-stressed Nile tilapia. The Bayesian hierarchical framework was used to pool and compare the effect sizes of growth parameters such as weight gain, feed intake, and feed conversion ratio (FCR). Furthermore, the surface under the cumulative ranking curve (SUCRA) was obtained to calculate the probability that each lipid source was the most effective against cold stress. All subsequent numbers refer to comparisons with diets containing only fish oil. Dietary Aurantiochytrium significantly increased weight gain (SMD = 2.00, CrI: 0.70 to 3.40). In contrast, diets containing coconut oil led to significantly lower weight gain (SMD = - 3.30, CrI: - 6.00 to - 0.63) and higher FCR (SMD = 17.0, CrI: 6.70 to 27.0). Additionally, dietary corn oil was associated with a decrease in feed intake (SMD = - 2.32, CrI: - 3.91 to - 0.80), while a combination of fish and corn oil reduced FCR (SMD = - 5.70, CrI: - 11.0 to - 0.81). In general, the analysis of SUCRA values revealed that in cold-stressed Nile tilapia, Aurantiochytrium, sunflower oil, and the combination of fish and corn oil were the most effective lipid sources for improving growth at suboptimal temperatures. The results of the current study can serve as a basis for future studies that focus on the use of dietary lipid sources to mitigate cold stress in Nile tilapia.

The effects of two dietary synbiotics on growth performance, haematological parameters, and non-specific immune responses in Japanese eel (Anguilla japonica)

Feed additives have attracted increased attention in aquaculture due to their ability to modulate fish gut microbiota, resulting in improved fish growth and immunity. This study assessed two synbiotics' effects in Japanese eels: Bacillus subtilis with mannooligosaccharide (MOS) and Enterococcus faecium with fructooligosaccharide (FOS). Six diets, including a control (CON), oxytetracycline (OTC), and four synbiotic diets - B.subtilis at 1 × 106 and 107 CFU/g with 5 g/kg MOS (BS6MO and BS7MO) and E. faecium at 1 × 106 and 107 CFU/g with 5 g/kg FOS (EF6FO and EF7FO) - were fed to triplicate groups of 20 fish averaging 6.00 ± 0.07g for eight weeks. Fish fed the BSMOS diets showed significantly higher weight gain (WG), specific growth rate (SGR), and feed efficiency (FE) compared to the CON and OTC diets (P < 0.05), but not significantly different from those fed the EFFOS diets. Weight gain, SGR of fish fed EFFOS were not significantly different from those fed all other diets (P > 0.05). Fish fed the OTC diet showed a higher mean aspartate aminotransferase (AST) level, though the difference was not statistically significant. The myeloperoxidase (MPO) activity of fish fed the BS7MO diet was significantly higher than in all other diets, and the superoxide dismutase (SOD) activity of fish fed the BS7MO diet was also significantly higher than in the EF7FO diet. Overall, the BSMOS synbiotic diets were significantly more effective than the CON diet in enhancing fish survival against Vibrio anguillarum. Our findings suggest that synbiotics can be a preferable alternative to antibiotics in aquaculture.

Evaluation of the Optimal Protein Required in Granulated Microdiets for Rockfish (Sebastes schlegeli) Larvae

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%.