Effects of soybean oligosaccharides on lipid metabolism of Japanese flounder (Paralichthys olivaceus Temminck et Schlegel) fed animal or plant protein source-based diets

Abstract

A feeding trial was conducted to investigate the effects of dietary soybean oligosaccharides (SBOS) on the levels of cholesterol in plasma and liver, and the fatty acid composition in muscle and liver of juvenile Japanese flounder (Paralichthys olivaceus Temminck et Schlegel). Four isonitrogenous and isocaloric practical diets (crude protein 49%, gross energy 19 kJ/g) including only fish meal (FM) or soy protein isolate (SPI) as sole dietary protein source with (Diets FMO and SPIO) or without (Diets FM and SPI) supplemented SBOS (stachyose, 2.61%; raffinose, 0.61%) were formulated. Each diet was randomly assigned to triplicate aquaria stocked with 30 fish (initial body weight 1.93±0.02 g) each. Fish were maintained in the flow-through aquaria at water temperature ranging from 22.0 to 25.0 and fed twice (08:00, 16:00) daily to apparent satiation for 8 weeks. Dietary SBOS supplementation significantly increased the levels of total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C) in plasma of the fish fed FM-based diets (P<0.05), but no significant differences were observed at the levels of plasma triacylglycerol (TG) and low-density lipoprotein cholesterol (LDL-C) and LDL-C/HDL-C ratio (P>0.05). The levels of TC, TG, HDL-C and LDL-C, and LDL-C/HDLC ratio in plasma of the fish fed SPI-based diets were not significantly influenced by the supplemented SBOS (P>0.05). Supplementation of SBOS did not influence the hepatic TC, TG and lipid contents and lipid droplet accumulation in fish fed FM-based diets, but significantly decreased the hepatic TC, TG and lipid contents and lipid droplet accumulation in fish fed SPI-based diets (P<0.05). In contrast, supplemented SBOS significantly increased fecal cholesterol extraction in the fish fed FM-based diets (P<0.05), but no significant difference was observed in the fish fed SPI-based diets (P>0.05). The fatty acid composition in muscle and liver was not significantly affected by supplemental SBOS regardless of dietary protein source (P>0.05). These results indicate that dietary SBOS supplementation (stachyose, 2.61%; raffinose, 0.61%) does not negatively affect the lipid metabolism of the fish fed FM-based diets, but decrease the incidences of fatty liver of the fish fed SPI-based diets.