THE EFFECT OF DIETARY BETA GLUCAN SUPPLEMENTATION ON THE INNATE IMMUNE RESPONSES OF NILE TILAPIA

To reduce susceptibility to stressors and diseases, immune-modulators such as β-glucans have been proven to be effective tools to enhance the innate immune responses of fish. Algamune^TM is a commercial additive produced from Euglena gracilis and it is a source of β-1,3-glucan. A trial was conducted to evaluate the immuno-modulation of dietary supplementation of Algamune (0, 100, 200, 400 and 800 mg kg^-1 of dry diet) for tilapia. Fish were fed twice daily during 3 weeks and feed was adjusted weekly according to body weight. At the end of the trial, fish were sampled for blood and head kidney, and the remainder of fish were challenged with a virulent strain of Streptococcus iniae. No differences were detected in growth parameters or innate immune responses such as reactive oxygen species of whole blood leukocytes, plasma lysozyme activity, hemolytic activity, total immunoglobulin of plasma and macrophage intracellular anion superoxide production. However, macrophage extracellular superoxide anion production was significantly (P<0.01) elevated in fish fed diets with 200 mg Algamune^TM kg^-1 or greater when compared to fish fed the basal diet. Results from the disease challenge did not show any statistical differences due to dietary treatment, although fish fed the diets supplemented with Algamune^TM at 100 and 200 mg/kg had the lowest numerical mortality values (Fig. 1). This study demonstrated that dietary supplementation of Algamune^TM had some immunostimulatory effects in tilapia.