Effects of cottonseed protein concentrate on growth performance, hepatic function and intestinal health in juvenile largemouth bass, Micropterus salmoides

Abstract

The study aimed to evaluate the effect of replacing fish meal (FM) by cottonseed protein concentrate (CPC) on growth, immune respone and health status of largemouth bass, Micropterus salmoides. Fish (initial body weight: 12.21 ± 0.15 g) were fed five isonitrogenous and isolipid diets (48% crude protein and 12% crude lipid) with CPC replacing 0 (control, CPC0), 15% (CPC15), 30% (CPC30), 45% (CPC45) or 60% (CPC60) of fishmeal for 8 weeks. The results showed that weight gain, specific growth rate and protein efficiency ratio were not appreciably reduced until more than 30% of the FM protein was replaced with CPC. Fish fed CPC60 diet had the lowest hepatic antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; glutathione peroxidase, GPX) activities and genes (SOD, CAT, GSH-Px) expression, but the highest malondialdehyde (MDA) level. Moreover, CPC60 diet significantly down-regulated the expression of anti-inflammatory genes (IL-10, TGF-β) and protein metabolism genes (P13K, AKT, m-TOR, S6K1), whereas up-regulated the expression of pro-inflammatory genes (IL-8, IL-1β, TNFα). Accordingly, the liver histological investigation showed that the histopathological alterations were dramatically increased in the CPC60 group compared to control and CPC30 group. In addition, the CPC60 group decreased the villi height and goblet cell number, and increased villi width and muscular thickness in midgut and hindgut compared with the other groups, respectively. Meanwhile, plasma diamine oxidase (DAO) activity, D-lactate and endotoxin contents increased markedly as the proportion of CPC increased. Notably, the increased dietary CPC levels down-regulated the expression of ZO-1, Claudin-1 and Occludin in intestine. The lower SOD, CAT activities and mRNA levels in intestine were also observed in CPC60 group. Broken-line model analysis based on WG against dietary CPC replacement level indicated that the optimum replacement level was 18.44% when supplemented with crystalline methionine and lysine. However, including too high proportion of CPC could suppress immune and antioxidant capacity, impair both the liver and intestinal health, and finally reduced growth of Micropterus salmoides.