Effect of dietary β-glucan on growth, survival and regulation of immune processes in rainbow trout (Oncorhynchus mykiss) infected by Aeromonas salmonicida

The present study evaluated the effects of dietary β-glucan (0, 0.05%, 0.1%, and 0.2%) on growth performance after 42 days of feeding. Thereafter, rainbow trout (Oncorhynchus mykiss) were infected with Aeromonas salmonicida, and survival rates as well as the regulating processes of stress- and immune-related factors were analyzed. In general, higher dietary β-glucan levels obviously improved specific growth rate (SGR), weight gain (WG) and feed efficiency (FE) (P ≤ 0.05). Survival rates in β-glucan groups increased significantly compared with the control group after A. salmonicida infection (P ≤ 0.05). Serum total superoxide dimutase (T-SOD), peroxidase (POD) as well as catalase (CAT) activities, and their mRNA expressions in the head kidney of fish in the β-glucan groups generally increased to higher levels after infection, and more quickly, compared with in the control group. Serum lysozyme (LSZ) and its expression in the head kidney in β-glucan groups reached a higher peak earlier than in the control group. Serum glutamic oxalacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) levels in the β-glucan groups were significantly lower than in the control group (P ≤ 0.05). The peak of heat shock protein 70 (HSP70) expression in the 0.2% β-glucan group was higher and occurred earlier than in other groups (P ≤ 0.05). These results confirm that 0.1% and 0.2% dietary β-glucan are beneficial for promoting growth in rainbow trout and enhancing resistance against A. salmonicida. Furthermore, β-glucan could play an important role in regulating stress- and immune-related factors in rainbow trout to more quickly fight against bacterial infection. •Dietary β-glucan in dosage of 0.1% and 0.2% can enhance growth performance of rainbow trout.•β-glucan from 0.05% to 0.2% is able to significantly enhance resistance to A. salmonicida in rainbow trout.•It can stimulate immune factors more quickly to higher levels to fight against bacteria.•In this paper, the optimal level of dietary β-glucan concentration for rainbow trout is 0.2%.