Improving productivity in aquaculture demands maintaining the well-being of the cultured organisms. For this purpose, probiotics have become common in culture setups to enhance fish growth, health, and resilience. The current study examined a novel marine bacterium for its feasibility in improving the growth, feeding, and health performances of gilthead seabream Sparus aurata. For this aim, a feeding trial was performed over 12 weeks in which fish were fed commercial aquafeed with different inoculation rates of the probiotic bacterium of 1x108, 1x1010, and 1x1012 CFU/Kg compared to a probiotic-free diet control. Fish growth rate and yield, digestibility, digestive enzyme activity, immune response, and microbial community composition were measured throughout the culture period. Sequentially, trials to examine feed digestibility fish resilience when challenged with pathogenic Streptococcus agalactiae were conducted using identical diets.
Results indicated no effect of probiotic treatment on fish growth performances, but protein and lipid digestion was improved when the probiotic was supplemented at 1x1010 CFU/Kg, proposing an improved absorption of these macronutrients. The probiotic supplement at 1x1010 CFU/Kg also induced an increase in antiprotease activity, while myeloperoxidase activity increased only during the first six weeks. Probiotic supplementation influences microbial community composition, indicating their resilience to varying treatments. Last but not least, the probiotic treatment improved fish survival after challenging them with Streptococcus agalactiae, with highest survival rate of 70% in the probiotic supplementation level of 1x1012 CFU/Kg. Overall, the novel probiotic bacterium efficiently improves feed digestion and fish health. The origin of such bacterium, from the gut of an algivorous sea urchin, proposes further study concerning the contribution to fish in feed digestion and energy gaining under diets with high plant or algal- ingredients.