Biofloc technology involves the manipulation of the culture system’s carbon: nitrogen ratio to promote bacterial community growth to convert toxic nitrogenous wastes and organics into functional microbial protein; this protein can then be used as a food source and mediate water quality. Biofloc systems have several advantages, which include improved biosecurity, feed conversion, water use efficiency, and nutrient processing. Analyzing the nutritional value and the relationship between high production of aquacultural practices using biofloc is essential. Many studies have demonstrated that biofloc increases the growth of aquatic species by acting as a food source or providing bioactive compounds. Other than this, the beneficial micro-organisms in biofloc systems contain compounds such as organic acids that could resist the growth of pathogenic microbes. They will also serve as a natural probiotic and increase the immunity and survival of fish and shrimp. This technology could be useful for further integration within many aspects of aquaculture production when microbial interactions are considered. However, future studies must fully understand the principles and mechanisms behind the benefits of interactions between biofloc and cultured fish and crustacean species.

This study was conducted to evaluate the individual and combined effects of long-term feeding of diets containing two probiotic Bacillus subtilis group strains (Aqua NZ and AP193) and the prebiotic Previda^®, a commercial hemicellulose extract, on growth performance, immune parameters and Aeromonas hydrophila susceptibility of juvenile Nile tilapia, Oreochromis niloticus. Nile tilapia of average weight 7.47 ± 0.11 g were fed diets formulated with the probiotics and/or the prebiotic, or a control diet for 8 weeks and, subsequently, challenged with A. hydrophila by intragastric gavage at a dosage of 3.9 × 10⁷ CFU per fish. Fish attained a mean weight of 59.5 ± 0.99 g at the end of the growth period. Under the conditions of the present trial, none of the diets significantly improved mean per cent weight gain (P = 0.70), thermal growth coefficient (P = 0.88) or feed conversion ratio (P = 0.87) of Nile tilapia. Except for the diet containing the prebiotic Previda^® only (P = 0.17), all other diets resulted in significantly higher fish survival compared to the control (P < 0.05). The combined effect of the prebiotic and probiotic strains emerged as the most important diet with respect to mortality reduction. The mean lysozyme and respiratory burst activities did not show any significant differences between treatments and control (P = 0.14 and 0.32, respectively). Thus, these probiotic strains used in this study have the potential to prevent disease due to A. hydrophila in O. niloticus.