Dietary administration of chitooligosaccharides to enhance growth, innate immune response and disease resistance of Trachinotus ovatus.

The present study was conducted to investigate the effects of dietary chitooligosaccharides (COS) supplementation on the innate immune response and protection against Vibrio harveyi infection in Trachinotus ovatus. A basal diet was supplemented with 0.0 (control), 2.0, 4.0 and 6.0 g COS kg(-1) to formulate four experimental diets. Each diet was randomly allocated to triplicate groups of fish in floating sea cages (1.5 × 1.0 × 2.0 m), and each cage was stocked with 80 fish (initial average weight 10.8 ± 0.05 g). After 8 weeks of feeding trial, Both the final weight and specific growth rate (SGR) significantly increased with increasing dietary COS levels up to 4.0 g kg(-1), whereas there were no significant differences for COS levels from 4.0 to 6.0 g kg(-1). A decreased feed conversion ratio (FCR) was observed with increasing dietary COS levels. The total leukocyte counts (WBC), differential leukocyte counts, respiratory burst activity, lysozyme and superoxide dismutase (SOD) activity were significantly increased with the increased levels of dietary COS (P < 0.05), and reached a maximum at level of 4.0 g kg(-1) COS. There were no significant differences in those immunological parameters between 4.0 and 6.0 g kg(-1) COS. Moreover, the dietary COS supplementation groups also exhibited a decrease in the cumulative symptom rates compared to the controls when challenged with V. harveyi. These results indicated that dietary intake containing COS could enhance the immune responses of fish and improve its resistance to infection by V. harveyi. Especially supplementation with 4.0 g kg(-1) COS to the fish for 56 days showed considerable improvement in the growth, survival and immune response of the fish.