Effects of dietary 1,8-cineole supplementation on physiological, immunological and antioxidant responses to crowding stress in rainbow trout (Oncorhynchus mykiss)

The aim of the present study was to investigate beneficial effects of dietary 1,8-cineole (cineole) supplementation on physiological, immunological and antioxidant responses of rainbow trout (Oncorhynchus mykiss) to crowding stress. The fish were fed for 50 days with diets containing 0 (control), 0.05, 0.1, 0.25, 0.5 and 1% cineole prior to exposure to a 14-day crowding stress. Serum stress markers (cortisol, glucose, lactate, T-4 and T-3), antioxidant responses [catalase (CAT) and superoxide dismutase (SOD) activities and total antioxidant capacity (TAC) and malondyaldehyde (MDA) levels] and immune responses [lysozyme and alternative complement (ACH50) activity, and total immunoglobulin (Ig) levels], and blood leukocyte (WBC) and differential counts were measured before and after crowding stress. Results showed that 1% cineole was capable to reduce the basal and stress-induced cortisol elevation and increase the serum T-3 levels after stress. Increase in dietary cineole levels significantly decreased serum cortisol, glucose and lactate levels. Increase in dietary cineole levels significantly increased serum CAT, SOD, lysozyme and ACH50 activities, and TAC and eosinophil levels, and decreased MDA and monocyte levels. After the stress, there was no significant difference in the control group CAT and SOD activities compared to the basal values; however, CAT activities decreased and SOD activities increased in the cineole-treated groups compared to the basal values. Nevertheless, the control group had significantly lower CAT and SOD activities compared to the fish treated with 0.1-1% cineole. Cineole significantly increased blood WBC and serum lysozyme, ACH50 and total Ig. Moreover, cineole administration significantly mitigated the stress-induced decrease in total Ig levels as well as increase in leukocyte count. The cineole-treated fish had higher survival and growth performance compared to the control group. Although all levels of cineole (0.05-1%) showed beneficial effects on different tested factors, 0.5 and 1% levels had beneficial effects on most of the tested factors; thus, are recommended for dietary inclusion to suppress adverse effects of stress in trout.