A 10-week feeding trial was conducted to investigate the effects of dietary bile acids (BA) on growth, glucose and lipid metabolism, liver histopathology, and the underlying regulation mechanism on AKT/FOXO1 (forkhead box O1) and cAMP/AMPK/SREBP1 (sterol regulatory element-binding protein 1) pathway in largemouth bass (Micropterus salmoides) fed with a high starch diet. Six experimental diets were prepared with BA levels at 0 (B0), 80 (B80), 160 (B160), 240 (B240), 300 (B300), and 600 (B600) mg/kg in a basal diet with 18.7% starch. Each diet was fed to six replicates with 30 fish (6.17 ± 0.03 g) in each tank. The highest weight gain rate (WGR) was observed in B300 group and the optimal level of BA was estimated at 475 mg/kg by a monistic cubic equation regression analysis. Dietary BA inclusion decreased hepatosomatic index (HSI) and hepatic lipid content significantly. The fish in B300 group clearly showed alleviated hepatic fibrosis, but more steatohepatitis symptoms diagnosed with various histopathological and immunofluorescence analysis. 10 out of 12 samples were observed hepatic fibrosis in B0 group while only two fibrosis samples in B300 group. The promoted liver histopathology by dietary BA was related to improved glucose and lipid metabolism. Dietary BA inhibited the expression of G6Pase by activating AKT and reducing FOXO1 transcription, which improved the regulation ability of gluconeogenesis, activated cAMP/AMPK and repressed SREBP1 transcription to inhibit hepatic lipogenesis, which prevented hepatic lipid accumulation. In conclusion, dietary BA enhanced the growth and alleviated liver fibrosis induced by a high starch diet to steatohepatitis/recovery symptom via improving glucose and lipid metabolism, which regulated by AKT/FOXO1 and cAMP/AMPK/SREBP1 pathway in largemouth bass.

A meta‐analysis of literature data on essential amino acid (EAA) requirements of fish and crustaceans was performed to re‐estimate EAA requirements and provide ideal amino acid profiles. Large numbers of studies have been conducted on EAA requirements of fish and crustaceans over the past decades. However, estimated EAA requirements of different species showed a large variation due to differences in methodological approaches and regression models. An extensive search and inclusion of literature on EAA requirements were conducted following the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses guidelines in this study, resulting in a dataset of 358 studies covering 77 species. The relative percentage of maximum weight gain was used as the outcome to evaluate the 10 EAA requirements. Forest plots analysis was employed for heterogeneity analysis, study weight allocation and re‐estimation of the requirements. Results showed that trophic level, water temperature and dietary EAA inclusion levels affected EAA requirements estimation. The meta‐analysis suggested that the estimated 10 EAA requirements (expressed as % crude protein, CP) of the fish were: arginine (Arg) 5.0 (±0.14), histidine (His) 2.0 (±0.11), isoleucine (Ile) 3.3 (±0.16), leucine (Leu) 4.9 (±0.24), valine (Val) 3.8 (±0.11), lysine (Lys) 5.2 (±0.12), sulfur amino acids (Met + Cys) 3.5 (±0.18), total aromatic amino acids (Phe + Tyr) 6.2 (±0.12), threonine (Thr) 3.5 (±0.18) and tryptophan (Trp) 0.9 (±0.08). Estimated EAA requirements (expressed as % CP) of crustaceans were Arg 5.1 (±0.31), His 2.5 (±0.15), Ile 4.3 (±0.97), Leu 5.7 (±0.08), Val 4.3 (±0.30), Lys 4.9 (±0.28), Met + Cys 3.2 (±0.18), Phe + Tyr 5.1 (±0.65), Thr 3.8 (±0.04) and Trp 0.8 (±0.15).

Clostridium autoethanogenum protein (CAP) is a new single-cell protein source originating from inactivated bacteria. An in vitro digestion experiment and an 8-wk growth experiment were conducted to evaluate the molecular weight distribution of the CAP hydrolysate, and the effects of dietary CAP levels on the growth performance, plasma parameters, hepatic and intestinal health, and the diversity of gut-adherent microbiota of largemouth bass (Micropterus salmoides). The fish (initial body weight of 47.99 ± 0.01 g) were fed diets where CAP gradually replaced 0% (CAP0), 12.5% (CAP12.5), 25% (CAP25), 37.5% (CAP37.5) and 50% (CAP50) of low-temperature steam dried anchovy fish meal (LTFM) in the diet. Results showed that the content of peptides below 1,000 Da in the CAP hydrolysate (0.56 mg/mL) was higher than that of the LTFM hydrolysate (0.48 mg/mL). Dietary CAP inclusion had no negative effect on growth performance, while whole-body lipid content significantly reduced in the CAP25 and CAP50 groups (P < 0.05). The plasma alanine aminotransferase activities and triglyceride concentrations in the CAP inclusion groups were significantly lower than those in the CAP0 group (P < 0.05). The plasma aspartate aminotransferase activity was significantly reduced in the CAP37.5 group (P < 0.05). The richness and diversity of the gut-adhesive microbiota and the proportion of Clostridium sensu stricto 12 in the CAP50 group were significantly higher than those in the CAP0 group (P < 0.05). Dietary CAP inclusion inhibited inflammatory responses by down-regulating the mRNA levels of interleukin 1β (IL1β), IL10 and transforming growth factor β1 (P < 0.05) in the liver. The mRNA levels of acetyl-CoA carboxylase 1 were significantly down-regulated in the CAP12.5, CAP25 and CAP37.5 groups (P < 0.05), while that of fatty acid synthase was significantly down-regulated in the CAP50 group (P < 0.05). These results demonstrate that dietary CAP inclusion could improve the hepatic and intestinal health of largemouth bass, and can be helpful to further develop CAP as a functional feed ingredient.