Taurocholate supplementation attenuates the changes in growth performance, feed utilization, lipid digestion, liver abnormality and sterol metabolism in turbot (Scophthalmus maximus) fed high level of plant protein

Inclusion of plant ingredients in carnivorous fish feeds is often associated with decreased lipid digestibility, reduced bile acid levels and hypocholesterolaemia, which may result in lower growth performance and feed utilization. The present study aimed at evaluating the effects of dietary taurocholate supplementation in turbot (Scophthalmus maximus) fed high levels of plant protein and gaining further insight into how cholesterol and bile acid metabolism is modulated by taurocholate. A 56 day feeding trial was conducted using juvenile turbot (initial weight 8.5 g) fed one of three isonitrogenous and isolipid diets: a fish meal diet (FM), a plant protein meal based diet (a mixture of 40% soybean meal and 16% wheat gluten meal, named as PP) and a taurocholate supplemented diet (0.5% supplemented in PP, named as C-tau). Compared with fish fed the FM diet, the fish fed the PP diet had significantly lower growth performance, feed utilization, hepatosomatic index (HSI) and more atrophied hepatocytes. PP diet also induced enteritis in the distal intestine. Lipid digestion and metabolism was depressed as indicated by decreased whole body lipid content, lipid digestibility, pancreatic lipase activity and cholesterol and total bile acids (TBA) levels. Except the distal intestinal histology, all these tested parameters of fish fed the C-tau diet were significantly higher than those of fish fed the PP diet. Furthermore, the HSI, whole body lipid content, lipid digestibility and TBA levels of C-tau fed fish were similar to those of FM fed fish. Regardless of taurocholate, dietary plant protein could significantly increase the expression of HMG-CoA reductase (hmgcr) and decrease the hepatic cholesterol 7 alpha-hydroxylase (cyp7a1). Compared with the fish fed PP diet, taurocholate supplementation significantly increased the expression of cyp7a1, but had no effect on hmgcr expression. In conclusion, dietary supplementation with taurocholate attenuated the plant protein meal induced negative effects on growth performance, feed utilization and lipid digestion and metabolism. In addition, the cholesterol and TBA-increasing effects of taurocholate could possibly be attributed to an improved digestion and absorption of cholesterol and TBA synthesis due to the up-regulation of cyp7a1 expression. Statement of relevant: Dietary taurocholate is useful for fish meal sparing (C) 2016 Elsevier B.V. All rights reserved.