Effects of dietary essential fatty acid requirements on growth performance, fatty acid composition, biochemical parameters, antioxidant response and lipid related genes expression in juvenile Onychostoma macrolepis

Abstract

This study was conducted to elucidate effects of dietary essential fatty acid requirements on the growth, physiological characteristics and expressions of some lipid-related genes in juvenile Onychostoma macrolepis. Seven isonitrogenous and isoenergetic purified diets containing tristearin (control group), 2% linoleic acid (LA), 2% α-linolenic acid (LNA), 1% LA + 1% LNA, 1% eicosapentaenoic acid (EPA), 1% docosahexaenoic acid (DHA) and 0.5% EPA + 0.5% DHA were formulated to feed juvenile O.macrolepis (initial body weight:1.51 ± 0.05 g) for eight weeks. The weight gain (WG), specific growth rate (SGR) and feed efficiency (FE) of the fish were significantly higher in the LNA group and the EPA + DHA group than in the control group (P < .05). The growth and feed utilization of the fish in the LNA group were similar to those in the EPA + DHA group. The highest levels of 18:2n-6, 18:3n-3, 20:5n-3and 22:6n-3 in muscle and liver were found in the LA group, the LNA group, the EPA group and the DHA group, respectively. The highest concentrations of serum cholesterol (CHOL) and triglyceride (TG) were observed in the fish fed on the LA diet, and there were no significant differences in serum CHOL and TG between the LA group and the LA + LNA group. Serum malondialdehyde (MDA) content was observed to be the highest in the EPA group, DHA group and EPA + DHA group, and significantly higher in the these groups than in the other groups (P < .05). In liver, the superoxide dismutase (SOD) activities and the malondialdehyde (MDA) content were found to be significantly the lowest and the highest in the EPA, DHA and EPA + DHA groups (P < .05). The body fat content of the fish fed on the LA diet was significantly higher than those of the control ones (P < .05). The fatty acid synthetase (FAS), acetyl-CoA carboxylase 1(ACC1) and sterol regulatory element binding protein-1 (SREBP-1) genes involved in the anabolic pathway had the highest expression levels in the LA group. The adipose triglyceride lipase (ATGL), carnitine palmitoyl transferase 1 (CPT1) and peroxisome proliferators-activated receptor α (PPARα) genes involved in the catabolic pathway had the lowest expression levels in the control group. These results showed that the increase in fish body fat content induced by the LA diet was related to the up-regulation of some lipid biosynthesis metabolism genes. This study recommended that the dietary requirement of fatty acids for the optimal growth and health of juvenile O.macrolepis be 2% LNA or 0.5% EPA + 0.5% DHA (approximately 9% dietary fat). Its results might be conducive to optimizing fish diets while designing optimum dietary fatty acid profiles and proportions.