Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2004
Publication Date: 6/1/2005
Citation: Whittington, R., Lim, C.E., Klesius, P.H. 2005. Effect of dietary ß-glucan levels on the growth response and efficacy of streptococcus iniae vaccine in nile tilapia, oreochromis niloticus. Aquaculture 248: 217-225. Interpretive Summary: Streptococcus iniae is a hemolytic, gram-positive bacterium that has been associated with outbreaks of disease in freshwater and marine fish species. To resolve this problem, a vaccine that gives good protection against streptococcal disease has been developed at our laboratory to reduce the risk of disease outbreaks in cultured and wild fish populations. The efficacy of vaccine can be enhanced by feeding fish diets containing compounds that increase fish immune responses. Thus, this study was conducted to determine if ß-glucan (structural component of the bacterial cell membrane and plants that have been shown to stimulate immunity by increasing resistance to infectious pathogens) can enhance vaccinated and non-vaccinated Nile tilapia. Results of this study indicated that, at the levels used, dietary ß-glucan had no effect on the growth performance of immunized and non-immunized juvenile Nile tilapia. Immunization with S. iniae ARS-98-60 vaccine alone resulted in the enhancement of specific protection of Nile tilapia against S. iniae infection. ß-glucan was not beneficial in improving immune responses and resistance of tilapia against S. iniae infection.
Technical Abstract: A feeding study was conducted to determine the effect of dietary ß-glucan levels on the growth performance, immune responses and resistance of immunized and non-immunized Nile tilapia (Oreochromis niloticus) to Streptococcus iniae challenge. Fish were fed a 32% protein commercial diet for a total period of 14 weeks. Weight gain and survival after 10 weeks of feeding did not significantly differ among treatments. Feed efficiency ratio (FER) of fish fed the 200-mg ß-glucan diet was slightly but significantly lower than those of the groups fed other diets. Immunization alone and the combination of ß-glucan and immunization had no effect on the parameters previously mentioned. Serum lysozyme activity at 14 days PC significantly decreased in fish fed the highest dietary ß-glucan level but was not affected by immunization and the interaction between ß-glucan and immunization. Specific immune responses were not affected by dietary ß-glucan and the interaction between ß-glucan and immunization, but the effects of immunization on these parameters were positive. Antibody responses at days 21 PBI and 14 PC were significantly enhanced by immunization with S. iniae vaccine, leading to increase protection against S. iniae infection. ß-glucan had no effect on stimulating the specific antibody response and resistance of immunized and non-immunized fish against S. iniae.