Partial substitution of fish meal by Clostridium autoethanogenum protein in the diets of juvenile largemouth bass (Micropterus salmoides)

The present study was conducted to investigate the effect of fish meal replacement with Clostridium autoethanogenum protein (CAP) on growth performance, haemato-biochemistry, digestive capacity, antioxidant index, and histopathological examination of liver and intestine in largemouth bass (Micropterus salmoides). Seven experimental diets were formulated with CAP replacement of 0% (CAP0), 15% (CAP15), 27% (CAP27), 39% (CAP39), 51% (CAP51), 63% (CAP63) and 75% (CAP75) fish meal, respectively. Results showed that replacement of fish meal by CAP did not affect SR, FBW, WGR, SGR and CF. While the fish fed diets containing CAP displayed a higher PER and a lower FCR than the control group (P < 0.05). However, the CAP inclusion level did not statistically affect the whole-body composition (P > 0.05). Additionally, The ADC of dry matter and protein were improved by addition of CAP (P < 0.05), while corresponding ADC of lipid were not significantly changed among different groups (P > 0.05). The lipase and amylase activities were not dramatically altered in stomach (P > 0.05), but were significantly increased in intestine with dietary substitution level up to 39% (P < 0.05). Differently, the protease activity of fish fed CAP75 was higher than other groups in stomach and intestine (P < 0.05). In addition, the activities of T-AOC and SOD in serum, liver and intestine were elevated with dietary CAP level (P < 0.05), whereas MDA content displayed the opposite trend. Moreover, the increased TP, ALB, TC, TG and AST/ALT were observed in treatment groups. In addition, the villus length and width of hindgut were dramatically increased with increasing dietary substitution level up to 39%. Furthermore, no adverse effect on the hepatic histology was occurred when fed diet with substitution level below 63%. Overall, the optimal CAP replacement level was 49.80% with maximum weight gain rate of juvenile largemouth bass.