Enhanced immune response and resistance to edwardsiellosis following dietary chitooligosaccharide supplementation in the olive flounder (Paralichthys olivaceus).

Abstract

This study was conducted to evaluate the effects of dietary chitooligosaccharide (COS) supplementation on peripheral leukocyte count, head kidney leukocyte phagocytic rate, phagocytic index, respiratory burst activity, serum lysozyme activity, and immune protection in Paralichthys olivaceus. A total of 300 flounder with an average body weight of 80-100 g were randomly assigned into four dietary groups: (I) basic diet (control), basic diet containing (II) 0.5% COS, and (III) 1% COS, fed continuously for 28 d, and (IV) basic diet containing 1% COS fed in 14 d intervals. Continuous feeding of 0.5% and 1% COS diets for 28 d significantly increased the number of peripheral leukocytes, head kidney leukocyte phagocytic rate, phagocytic index, respiratory burst activity, and serum lysozyme activity (P < 0.05 or P < 0.01). After a 10 d Edwardsiella tarda challenge, the immune protection rates in the 0.5% and 1% COS groups were 30% and 60%, respectively. No control fish survived the E. tarda challenge treatment. Most immune indices were slightly lower after removal of COS from the diet for 14 d, but all immune indices were observed to recover after another 14 d of COS supplementation. This study demonstrates that supplementation of a basic diet with COS enhances the non-specific immune response and improves survival rates following infection with E. tarda in P. olivaceus. An optimized interval feeding strategy with diets containing 1% COS may have potential applications in the prevention of disease in aquacultured P. olivaceus.