Interactive effects of dietary cholesterol and protein sources on growth performance and cholesterol metabolism of Japanese flounder (Paralichthys olivaceus)

A feeding trial was conducted to compare the effects of supplemental cholesterol in fish meal (FM), fish protein concentrate (FPC), soy protein isolate (SPI) and soy protein concentrate (SPC)-based diets on growth performance and plasma lipoprotein levels of Japanese flounder (Paralichthys olivaceus). Eight isonitrogenous and isocaloric diets including FM, FPC, SPI or SPC as sole protein source with or without supplementation with 10 g cholesterol kg-1 diet were fed to juvenile fish for 8 weeks. Dietary cholesterol supplementation significantly increased the feed intake and specific growth rate in fish fed SPI-based diets, but decreased those in fish fed FPC-based diets. In addition, cholesterol supplementation significantly increased the level of cholesterol and ratio of low-density lipoprotein cholesterol to high-density lipoprotein cholesterol in plasma of fish fed fish protein-based diets, whereas no effects were observed in fish fed soy protein-based diets. The hepatic lipid content of fish fed FPC-, SPI- or SPC-based diets were significantly increased by supplemental cholesterol, but no influence was observed in fish fed FM-based diets. These results suggested that dietary protein source modify the growth-stimulating action of cholesterol; cholesterol supplementation may increase the arteriosclerotic lesion in fish fed fish protein-based diets and the incidence of fatty liver in fish fed soy protein-based diets.