Effects of dietary eicosapentaenoic acid on the growth performance, fatty acid profile, immunity and heat tolerance of juvenile abalone Haliotis discus hannai Ino

Abstract

A 93-day growth trial was performed to evaluate the influences of graded dietary EPA levels (0.03% (control group), 0.24%, 0.63%, 1.07%, 1.72% and 2.25%) on the growth performance, immunity and heat tolerance of juvenile abalone Haliotis discus hannai with a mean initial weight of 4.15 ± 0.18 g. After the feeding trial, the findings found that the highest weight gain rate (WGR) belonged to the groups fed with 0.63% ∼ 1.72% of dietary EPA (P < 0.05). The lowest feed conversion ratio was distinguished in the groups with 0.63% ∼ 1.07% of dietary EPA (P < 0.05). Also, EPA supplementation in abalone feed increased the content of crude lipid in the soft body and the activity of lipase in the intestine (P < 0.05). The total antioxidative capacity increased when dietary EPA levels rose from 0.03% to 1.07%, and then decreased (P < 0.05). Furthermore, compared to the control group, the 0.24% and 0.24% ∼ 0.63% of dietary EPA significantly down-regulated the mRNA levels of IκB kinase and kelch-like ECH-associated protein 1, respectively (P < 0.05). However, nuclear factor-κB and interleukin 1 receptor-associated kinase 4 genes expression in the digestive gland were significantly up-regulated by the use of 1.72% and 2.25% of EPA in diet (P < 0.05). The mRNA levels of tumor necrosis factor α and interleukin 16 were significantly up-regulated by the 2.25% of dietary EPA (P < 0.05). The 1.72% of dietary EPA significantly increased the falling rate of abalone after the heat stress compared with the control (P < 0.05). In conclusion, the optimal dietary EPA requirement of juvenile abalone was determined as 1.36% based on quadratic regression analysis against WGR. Moderate dietary EPA content (0.63% ∼ 1.07%) improved the immunity and heat resistance of abalone. Excessive dietary EPA content (1.72% ∼ 2.25%) decreased the growth, meanwhile, increasing the oxidative stress, inflammation and susceptibility of abalone to heat stress.