Evaluation of dietary Heat-killed Lactobacillus plantarum strain L-137 supplementation on growth performance, immunity and stress resistance of Nile tilapia (Oreochromis niloticus)

Fish fed HK L-137 containing diets showed significantly higher growth compared to those fed the control diet. Phagocyte and lysozyme activity of fish fed HK L-137 diets were significantly higher than those of the control for 50-day feeding period and a similar situation obtained at day 75 for fish fed 4 ppm HK L-137-containing diets compared to those of the remaining diets (0 and 2 ppm HK L-137). Stress resistance in fish to ammonia indicated that fish fed HK L-137 supplemented diets performed a lower increment of cortisol concentration compared to those fed the control diet. Interestingly, the lowest cumulative mortality rate (78.33%) obtained in fish fed 20 ppm HK L-137 while the poorest values observed in group fed control diet (96.67%) after exposure to S. agalactiae for 15 days. The present study revealed that the appropriate doses of HK L-137 ranged from 20 to 50 ppm in diets provided the notable positive effects enhancing not only the growth performances but also immunity responses and stress resistance of Nile tilapia.