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This study aimed at evaluating the effects of dietary inclusion of Bacillus subtilis DSM 32315 on the growth, immunity, intestinal architecture and gut microbiota of juvenile largemouth bass Micropterus salmoides (LMB). B. subtilis DSM 32315 was supplemented in the diets at the levels of 0 (control, CON), 1.5 (BS1.5, 3 × 106 CFU/g feed) and 3 g/kg (BS3, 6 × 106 CFU/g feed). Each diet was assigned to four replicate tanks of LMB juveniles (initial mean body weight, 8.32 ± 0.06 g) with 20 fish per tank for 9 weeks. The results showed that the growth and feed utilization of LMB were not sensitive to dietary modifications (p > .05). Compared with the CON fish, dietary BS supplementation did not affect the haematological parameters (white and red blood cell counts and haematocrit value) of LMB (p > .05), but the BS1.5 fish performed better than the BS3 fish. Serum innate immunity indicators (lysozyme activity and complement C3 and C4 levels) were improved with dietary BS supplementation at both doses, while higher serum IgM level was only recorded at 1.5 g/kg feed (p < .05). All the sampled fish exhibited intact intestines, but the intestinal architecture (villus height and muscular layer thickness) still benefited from dietary BS inclusion at both doses (p < .05). Although intestinal anti‐inflammatory response (mRNA levels of IL‐10 and TGF‐β1) did not differ between the BS supplemented fish (p > .05), the BS1.5 fish obtained superior pro‐inflammatory response (mRNA levels of IL‐1β, IL‐8, and TNF‐α) over the BS3 fish (p < .05). Compared with the CON fish, the abundance of the harmful Plesiomonas shigelloides decreased in the gut microbiota of the BS1.5 fish (p < .05). Despite the BS3 fish obtained higher diversity of gut microbiota, the abundances of potential beneficial (Cetobacterium somerae and Shewanella xiamenensis) and harmful bacteria (Acinetobacter johnsonii and P. shigelloides) increased or decreased simultaneously (p < .05). Taken together, it was concluded that dietary BS DSM 32315 inclusion presented some positive effects on LMB. Although the BS1.5 fish performed better than the BS3 fish, the best supplemental dose need to be further studied.

This study was performed to evaluate the effects of dietary distinct protein to starch ratios on the growth, feed utilization, blood biochemistry, hepatic glucose metabolism and hepatocyte apoptosis of Nile tilapia Oreochromis niloticus. Three iso-lipidic (ca 6.56%) diets were formulated with elevated corn starch levels at the cost of protein provision, being designated as diets P40S5 (40.4% protein and 4.62% starch), P30S25 (30.4% protein and 24.2% starch) and P20S50 (19.9% protein and 48.6% starch). Tilapia juveniles (initial mean body weight, 32.0 g/fish) were assigned to 12 rectangular tanks (250 L each) with 20 fish per tank and fed the experimental diets to apparent satiation for 8 weeks. The results showed that either excess (40%) or insufficient (20%) amount of dietary protein impaired the growth of tilapia. Excess dietary protein led to unsatisfactory protein catabolism (lower protein efficiency ratio and protein productive value, and higher mRNA levels of hepatic glutamic-pyruvic transaminase 1 and glutamic-oxaloacetic transaminase paralogs), while insufficient amount of protein resulted in lower whole-body protein percentage. An increase in dietary starch from 5% or 25% to 50% was associated with enhanced lipid and glycogen storages in the liver of tilapia. Consistently, dietary starch reception up to 50% upregulated the expression of hepatic representative genes involved with glycolysis (glucokinase and phosphofructokinase muscle type a) and lipogenesis (acetyl-CoA carboxylase α and fatty acid synthase) while downregulated the expression of the gluconeogenic glucose-6-phosphatase catalytic subunit paralogs. TUNEL staining suggested that stronger apoptosis signal was recorded at the bile duct epithelium of the P20S50 fish.Concomitantly, plasma bile acid level nearly doubled, and an incidence (50%) of 'green liver' was observed in this treatment as compared with the P40S5 and P30S25 fish, indicating that bile acid metabolism disorder might be induced. Though plasma glucose (4.66-5.11 mmol/L) was not responsive to different treatments, advanced glycation end-products accumulated in the blood of the P20S50 fish, suggesting that 50% starch reception was probably associated with the progression of diabetes-associated | 6515 ZHU et al.

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