Effect of dietary arachidonic acid levels on growth performance, fatty acid profiles and lipid metabolism of juvenile yellow catfish (Pelteobagrus fulvidraco)

Abstract

An 8-week feeding trial was conducted to evaluate the effects of different dietary arachidonic acid (ARA) levels on growth performance, fatty acid composition, hepatic intermediary metabolism and antioxidant responses for juvenile yellow catfish. An ARA-enriched oil was supplemented into the basal diet to formulate six iso-nitrogenous and iso-energetic practical diets containing 0.03% (the control diet), 0.30%, 0.60%, 0.90%, 1.20% and 1.50% of dry weight. Dietary ARA levels were 0.39%, 2.47%, 4.96%, 7.49%, 9.79% and 12.64% total fatty acids, respectively. Triplicate groups of 20 fish (average initial weight is about 1.55±0.01g) were fed to apparent satiation twice daily. The results indicated that fish fed the diets containing 4.96% and 7.49% ARA of total fatty acids have higher final body weight and percent weight gain (PWG) than those fed the other diets. Survival, feed conversion ratio, hepatosomatic index and viscerosomatic index were not significantly influenced by the dietary ARA levels. Fatty acid compositions both in liver and muscle reflected closely those of fatty acid profiles in diets, ARA proportion in liver and muscle significantly increased with dietary ARA levels increasing from 0.39% to 12.64% of total fatty acids, while, EPA proportion in liver significantly decreased with increase of dietary ARA levels. Fish fed the control diet had the highest aspartate aminotransferase (AST) and glucose content in serum among all treatments, and fish fed the 9.79% and 12.64% ARA of total fatty acids had higher malondialdehyde (MDA) content in liver than those fed the other diets. However, the activities of total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-PX) and catalase (CAT) in liver were not significantly influenced by dietary ARA levels. The relative gene expression of accα, g6pd, 6pgd and evovl5 in liver down-regulated significantly with the dietary ARA levels increasing from 0.39% to 12.64% of total fatty acids. The relative gene expression of atgl and hslb in liver down-regulated significantly with the dietary ARA levels increasing from 0.39% to 7.49% of total fatty acids, and then up-regulated as dietary ARA levels increasing from 9.79% to 12.64%. However, relative gene expression of cpt1a and ppara in liver are down-regulated in ARA supplemental groups. These results suggested that dietary moderate ARA levels (4.96% and 7.49% of total fatty acids) could improve growth performance and antioxidant response, and up-regulate or down-regulate relative expression levels of some lipid metabolism-related gene in liver. Two slope broken-line regression analysis of PWG against dietary ARA levels indicated that optimal dietary ARA requirement for juvenile yellow catfish was 6.45% of total fatty acids.