Effects of dietary cholesterol on growth performance, feed intake and cholesterol metabolism in juvenile turbot ( Scophthalmus maximus L.) fed high plant protein diets

A 9-week growth trial was conducted to investigate the effects of dietary cholesterol supplementation on growth performance, feed intake and cholesterol metabolism of juvenile turbot ( Scophthalmus maximus L.) fed high plant protein diets. A fish meal diet (diet FM) with 58% FM was formulated, and this diet was used as control. The other four diets were formulated to contain 14.5% FM, 42.0% soybean meal (SBM), and 18.5% wheat gluten meal. The four diets were supplemented with 0.0%, 0.5%, 1.0% and 1.5% cholesterol, respectively, and were isonitrogenous and isolipidic to the diet FM. They were named as diet C-0.0%, C-0.5%, C-1.0% and C-1.5%, respectively. The final dietary cholesterol concentrations were 0.30%, 0.77%, 1.25%, and 1.78%, respectively. That in control diet was 0.63%. The results showed that weight gain rate (WGR) and feed efficiency rate in fish fed diet FM were significantly higher than those in fish fed other diets ( P < 0.05). Furthermore, compared with fish fed diet C-0.0%, fish fed diet C-1.0% significantly enhanced WGR, feed intake (FI) and cholesterol levels in plasma and liver. However, WGR and FI in fish fed diet C-1.5% were significantly lower than those in fish fed diet C-1.0% ( P < 0.05). Fish fed diet C-1.0% showed significantly higher whole-body lipid content than that of fish fed other diets ( P < 0.05). The total cholesterol (TC), free cholesterol (FC), cholesterol esters, high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) contents in fish plasma, TC and cholesterol esters in fish liver, and TC in fish feces were significantly correlated with dietary cholesterol contents, and correlated coefficients were above 0.74. Fish fed diet C-0.0% showed the lowest fecal total bile acid and activity of cholesterol 7α hydroxylase among dietary treatments. These results suggested that 1.25% of dietary cholesterol is helpful for juvenile turbot fed high plant protein diets to get significantly better growth rate without negative effects.