Uthpala Padeniya

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 × 10 ⁷ CFU g ¹ ) and BiOWiSH Feedbuilder Syn3 (BW; 3.6 × 10 ⁴ 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 × 10 ⁴ CFU g ⁻¹ (BWx1) and 7.2 × 10 ⁴ 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.

Aquaponics and biofloc‐based aquaculture systems are environmentally sustainable food production systems. When biofloc technology is combined with hydroponic systems, it expands economic diversity by producing additional value‐added products. Dietary additives were incorporated into fish feeds in this trial to improve food production in decoupled aquaponic systems. In this decoupled aquaponic system, the biofloc aquaculture system consisted of nine cylindrical tanks of 3750 L with 170 juvenile Nile tilapia (9.99 ± 0.54 g) stocked in each tank. The fish were randomly assigned to one of three treatment groups: fish fed a commercial feed (Com), commercial diet + protease complex (PC; AG175 by Jefo Nutrition; 175 g 1000 kg ⁻¹ ), and commercial feed + humic substance (HS; MFG50 by Kent Nutrition; 2500 g 1000 kg ⁻¹ ). The feeding trial was conducted for 60 days. A deep‐water culture hydroponic system with nine 109 L troughs was used. Each trough corresponded to each tank and contained 15 romaine lettuce plants. The first 4 weeks were fish growth trials, and the last four were fish and plant growth trials. Fish and plant growth parameters showed no differences between treatments. However, the leaf greenness in romaine lettuce plants in the PC treatment had significantly higher chlorophyll content than the other treatments ( p = 0.002). When microbial communities were analyzed, significant differences were found in the Shannon diversity indices (fecal, water, and root p < 0.001), Chao1 (fecal p < 0.002, water p < 0.001, and root p < 0.001), and observed species (feca; p = 0.046, water p = 0.017, and root p = 0.015). When beta diversity was analyzed through the Bray–Curtis dissimilarity index, fecal samples ( p = 0.001) and root samples ( p = 0.002) showed clear differences. The most abundant phyla found in all samples were Pseudomonadota. Overall, this study concluded that these additives did not affect the growth of Nile tilapia and romaine lettuce but influenced the bacterial composition of fish feces, water, and root samples and the chlorophyll content of the plants.

Biofloc technology is a rearing technique that maintains desired water quality by manipulating carbon and nitrogen and their inherent mixture of organic matter and microbes. Beneficial microorganisms in biofloc systems produce bioactive metabolites that may deter the growth of pathogenic microbes. As little is known about the interaction of biofloc systems and the addition of probiotics, this study focused on this integration to manipulate the microbial community and its interactions within biofloc systems. The present study evaluated two probiotics (B. velezensis AP193 and BiOWiSH FeedBuilder Syn 3) for use in Nile tilapia (Oreochromis niloticus) culture in a biofloc system. Nine independent 3785 L circular tanks were stocked with 120 juveniles (71.4 ± 4.4 g). Tilapia were fed for 16 weeks and randomly assigned three diets: a commercial control diet or a commercial diet top‐coated with either AP193 or BiOWiSH FeedBuilder Syn3. At 14 weeks, the fish were challenged with a low dose of Streptococcus iniae (ARS‐98‐60, 7.2 × 10⁷ CFU mL⁻¹, via intraperitoneal injection) in a common garden experimental design. At 16 weeks, the fish were challenged with a high dose of S. iniae (6.6 × 10⁸ CFU mL⁻¹) in the same manner. At the end of each challenge trial, cumulative per cent mortality, lysozyme activity and expression of 4 genes (il‐1β, il6, il8 and tnfα) from the spleen were measured. In both challenges, the mortalities of the probiotic‐fed groups were significantly lower (p < .05) than in the control diet. Although there were some strong trends, probiotic applications did not result in significant immune gene expression changes related to diet during the pre‐trial period and following exposure to S. iniae. Nonetheless, overall il6 expression was lower in fish challenged with a high dose of ARS‐98‐60, while tnfα expression was lower in fish subjected to a lower pathogen dose. Study findings demonstrate the applicability of probiotics as a dietary supplement for tilapia reared in biofloc systems.

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.