Evaluation of Probiotic Effects on the Growth Performance and Microbiome of Nile Tilapia (Oreochromis niloticus) in a High-Density Biofloc System.

Biofloc technology is an aquaculture production system that has gained popularity with tilapia production. Probiotics provide benefits for the host and/or aquatic environments by both regulating and modulating microbial communities and their metabolites. When a probiotic feed is combined with a biofloc system, the production amount may be improved through better fish growth, disease resistance, and/or improved water quality by reducing organic matter and stabilizing metrics such as pH and components of the nitrogen cycle. Two research trials measured Nile tilapia (Oreochromis niloticus) growth performance and composition of the microbial communities in the water and within the fish fecal material, following feeding with top-coated probiotic treatments. Trial A incorporated tilapia (71.4 ± 4.4 g), and a commercial diet (Control) that was top coated with either Bacillus velenzensis AP193 (AP193; 1 × 10⁷ CFU g¹) and BiOWiSH Feedbuilder Syn3 (BW; 3.6 × 10⁴ CFU g^-1). In Trial B, juvenile tilapia (5.34 ± 0.42 g) were fed treatment diets top coated with two different concentrations of BiOWiSH Feedbuilder Syn3 at final concentrations of 3.6 × 10⁴ CFU g^-1 (BWx1) and 7.2 × 10⁴ CFU g^-1 (BWx2). Tilapia were offered commercial feed (38% protein floating tilapia feed) as a control diet for both trials. Results from both growth trials indicated no differences in growth performance due to the probiotic additions, except for feed conversion ratio (FCR) in Trial B. Both BWx1 and BWx2 showed improved survival, water quality, solids management, and bacterial composition of water and fecal matter. Even though growth performance results presented no significant differences, results could differ based on the probiotic concentration, the route of probiotic administration, or their impact on the microbial community of the biofloc system culture water. Trial results indicated that testing on a larger scale with varied probiotic doses may be necessary to achieve an effective dosage for improving tilapia growth performance.