Effects of dietary sodium butyrate on growth,digestive enzymes,body composition and nutrient retention-related gene expression of juvenile yellow catfish (Pelteobagrus fulvidraco)

An 8-week feeding trial was conducted to evaluate the effects of sodium butyrate(SB)on growth,digestive enzymes,body composition and nutrient retention-related gene expression of juvenile yellow catfish(Pel-teobagrus fulvidraco).Five isonitmgenous and isolipidic diets(420 g/kg protein and 90 g/kg lipid)were formulated to contain 0(control),250,500,1,000 or 2,000 mg/kg SB.Triplicate groups of 40 fish(BW=1.26±0.01 g)per tank(300-L cylindrical fiberglass tanks)for each diet were fed to apparent satiation twice daily.Stomach,hepatopancreas and intestine samples were obtained for digestive enzymes activities analyses.A real-time quantitative PCR analysis was performed to determine the relative expression of target of rapa-mycin(TOR)and lipoprotein lipase(LPL)in the hepatopancreas and intestine.Fish fed the diets supplemented with SB at 500 and 1,000 mg/kg showed significantly higher specific growth rate and significantly lower feed conversion ratio compared to the control(P<0.05).Dietary SB inclusion did not alter activities of intestinal amylase,creatine kinase and sodium-potassium adenosine triphosphatase(Na+/K+-ATPase),but increased activities of hepatic trypsin,stomachic lipase,intestinal lipase,alkaline phosphatase and y-glutamyl trans-peptidase for fish fed 1,000 mg/kg SB compared to the control(P<0.05).Intestine length index,intestine somatic index,fold height and muscular thickness of distal intestine were significantly higher in 1,000 mg/kg SB groups compared to the control(P<0.05).Significantly higher levels of whole-body crude protein,ash,calcium,phosphorus,nutrition retention and relative mRNA of intestinal TOR were observed in 1,000 mg/kg SB group(P<0.05).Whole-body lipid content and hepatopancreas LPL mRNA expression in 2,000 mg/kg SB gmup were significantly higher than the control(P<0.05).Relative mRNA levels of intestinal LPL and hepatopancreas TOR were significantly higher in the 500 mg/kg SB group compared to those in other groups(P<0.05).The increased growth performance,digestive enzymes and nutrient retention in fish fed the diets supplemented with SB at 500 and 1,000 mg/kg suggests that SB can be a desirable growth promoter as an antibiotic alternative in diets.