Effects of dietary tributyrin supplementation in low fish meal diet containing high-Clostridium autoethanogenum protein on the growth performance, antioxidative capacity, lipid metabolism and intestinal microbiota of largemouth bass (Micropterus salmoides)

This study aimed to investigate the impact of dietary tributyrin (TB) in the low fish meal (high-Clostridium autoethanogenum protein, CAP) diet on the growth, antioxidation, lipid metabolism and intestinal microbiota of largemouth bass (Micropterus salmoides). For eight weeks, largemouth bass (15.05 ± 0.58 g) were fed on eight isonitrogenous and isolipid diets with graded levels of dietary TB (0 g/kg, 0.2 g/kg, 0.4 g/kg, 0.8 g/kg, 1.6 g/kg, 3.2 g/kg, 4.0 g/kg and 8.0 g/kg). The findings showed that the weight gain rate (WGR) and specific growth rate (SGR) were increased by 1.6 g/kg of dietary TB. The protein efficiency and deposition ratios were linearly affected by dietary TB. The broken-line model based on the WGR revealed that 1.617 g/kg of dietary TB was sufficient for optimal growth. The digestive enzyme activities and villus length of the intestine were increased by dietary TB (1.6 g/kg). Total antioxidant capacity (T-AOC), superoxide dismutase (SOD) and catalase (CAT) activities were significantly improved, and the malondialdehyde (MDA) and protein carbonyl (PC) contents were significantly decreased after dietary TB. The expressions of nuclear factor erythroid 2-related factor 2 (nrf2) and kelch like ech associated protein 1 (keap1) in the liver and intestine were significantly increased and decreased by 1.6 g/kg of dietary TB, respectively. The mRNA levels of copper-zinc superoxide dismutase (cuznsod), cat, heme oxygenase-1 (ho-1) and glutathione peroxidase (gpx) were significantly upregulated. Dietary TB could significantly affect the total protein (TP) and albumin (ALB) content in the serum. The aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were the lowest at 1.6 g/kg of TB group. Besides, the hepatocyte vacuolation and nuclear translocation were alleviated after supplementation of 0.2‰− 3.0‰ of dietary TB. The total cholesterol (T-CHO), high density lipoprotein cholesterol (HDLC) and low density lipoprotein cholesterol (LDLC) were significantly increased by dietary TB. The triglycerides (TG) content was decreased by dietary TB. The mRNA levels of sterol regulatory element-binding protein 1-c (srebp1-c), acetyl-coa carboxylase alpha (accα), fatty acid synthase (fasn) and accβ in the liver were significantly downregulated, and peroxisome proliferator-activated receptor alpha (pparα) and carnitine palmitoyltransferase 1 (cpt-1) were upregulated by 1.6 g/kg of dietary TB. Dietary TB had effects on the intestine microbes of largemouth bass. The Cetobacterium was present in the highest percentage and increased from 41% (0 g/kg TB) to 59% (1.6 g/kg TB). The Mycoplasmataceae was the second most predominant genus and decreased from 90% in the 0 g/kg of TB group to 10% in the 1.6 g/kg of TB group. In summary, the dietary TB could be supplemented in the CAP-based diet for better growth and antioxidation, lipid metabolism and intestinal microbiota of largemouth bass.