Impacts of dietary eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) level and ratio on the growth, fatty acids composition and hepatic-antioxidant status of largemouth bass (Micropterus salmoides)

Abstract

A ten-week feeding trial was conducted to evaluate largemouth bass (Micropterus salmoides, LMB) responses to supplemental eicosapentaenoic acid (EPA)- and docosahexaenoic acid (DHA)-rich oils at different inclusion levels and ratios. For this purpose, eight experimental diets were formulated to contain 42% crude protein and12% lipid. Two diets were formulated to be n-3 fatty acid (FA) and EPA/DHA depleted and served as negative controls for n-3 FA or EPA + DHA, respectively. Two additional sets of three diets were designed to contain 1 or 2% EPA + DHA and three different EPA:DHA ratios (20:80, 50:50, and 80:20). Each diet was fed to triplicate groups of 15 feed-trained juvenile LMB (13.8 ± 0.2 g initial weight) stocked in 110-L glass aquaria operating as a recirculating aquaculture system. At the end of the feeding trial, the production performance of LMB fed EPA + DHA supplemented diets was unaffected by EPA + DHA levels and ratios. However, LMB fed diets with either 1 or 2% EPA + DHA displayed higher weight gain and feed efficiency compared to those fed un-supplemented diets. HSI was lower groups fed n-3 FA depleted compared to 2% EPA + DHA-fed groups. No significant differences were detected for whole-body proximate composition of LMB; while whole-body EPA and DHA concentrations were significantly affected by diet. Liver antioxidant enzyme activities were unaffected by the dietary supplementation of 1 or 2% EPA + DHA, but liver superoxide dismutase activity was significantly higher in fish fed EPA/DHA depleted diet relative fish fed the n-3 FA depleted and 1% EPA + DHA diets. On the contrary, significantly lower malondialdehyde concentration was observed in the liver of LMB fed the latter relative to fish fed the former diet. Based on the overall findings, LMB appears to be able to synthesize EPA and DHA from linolenic acid to meet physiological needs for adequate production performance and health. Nevertheless, our findings also indicate that both weight gain and feed efficiency, as well as whole-body concentrations of EPA and DHA can be enhanced in LMB by the dietary provision of around 1% EPA + DHA.