Evaluation of the Dairy/Yeast Prebiotic, Grobiotic-A, in the Diet of Juvenile Nile Tilapia, Oreochromis niloticus

Two different feeding trials were conducted to evaluate the effects of dietary supplementation with the dairy/yeast prebiotic GroBiotic-A (GBA) to Nile tilapia diets. A nutritionally complete basal diet was supplemented with GBA at either 1 or 2% of dry weight, and all three diets were fed to triplicate groups of juvenile fish in two consecutive trials. Trial 1 continued for 8 weeks, while Trial 2 was conducted for 5 weeks to more specifically assess immunological responses, intestinal characteristics and disease resistance of tilapia. At the conclusion of Trial 1, there were no differences in weight gain (WG) or feed efficiency (FE) among fish fed the three diets. However, fish fed the diet with GBA at 2% had significantly increased survival and noticeably elevated levels of plasma lysozyme compared to fish fed the basal diet or the diet with GBA at 1%. Similarly, at the conclusion of Trial 2, WG and FE were unaffected by GBA supplementation; however, fish fed the diet with GBA at 2% also exhibited elevated plasma lysozyme as well as significantly (P < 0.05) increased levels of extracellular superoxide anion production (EX-SOAP) by macrophages. Dendrogram analysis of denaturing gradient gel electrophoresis (DGGE) images detected a significantly different microbial community within the intestine of fish fed the diet with GBA at 2% compared to fish fed the basal diet and diet with GBA at 1%. None of the experimental diets resulted in significant improvements to survival after exposure to Streptococcus iniae due to within treatment variability. However, fish fed the diet with GBA at 2% did tend to experience reduced mortality (12.5%) as compared to fish fed the basal diet (35%). Thus, supplementation of GBA at 2% of diet did alter the gut microbiota of tilapia and enhanced immunological responses and disease resistance to S. iniae.