Biofloc technology is a rearing technique that encompasses water quality by manipulating carbon and nitrogen and their inherent mixture of organic matter and microbes. Biofloc systems have several advantages, which include improved biosecurity, feed conversion, water use efficiency, and increased health and survival of rearing organisms. Beneficial micro-organisms present in biofloc systems contain compounds such as organic acids that may deter 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, such as adding probiotics to manipulate the microbial community and its interactions within biofloc systems.
In the present study, two probiotics (AP193 and BiOWiSH FeedBuilder Syn 3) are evaluated for use in Nile tilapia culture in a biofloc system. Nine individual circular tanks (1000 gallons) were stocked with 120 juveniles (71.4 ±4.4 g). Tilapia were randomly assigned 3 diet treatments: a commercial reference diet feed, commercial feed top-coated with AP193, and commercial feed top coated with Syn3. The trial was conducted for 15 weeks, and water quality parameters were kept at their standard limits. At the end of the feed trial, the fish were challenged with Streptococcus iniae (ARS-98-60, 6.6 x 108 CFU/mL, via intraperitoneal injection) in a common garden setup.
At 10 days post-infection, cumulative percent mortality (CPM) differed across the treatment groups. The CPM of the commercial diet-fed fish was 78±12 %, the AP193-fed fish was 35±8 %, and that of Biowish-fed tilapia was 18±11%. The mortality of fish that did not receive probiotics was significantly higher than AP193-fed fish (p=0.009) and Biowish-fed fish (p=0.003). These values indicate that adding probiotics to Nile Tilapia reared in biofloc systems enhances the disease resistance, and potential immune response against S.iniae. Serum lysozyme activity was also analyzed pre- and post- challenge. No differences were found between the dietary groups pre-challenge (p=0.29) and post challenge (p=0.21). To further discern the tilapia immune responses pre- and -post challenge, gene expression of pro inflammatory cytokines is still ongoing. Furthermore, the microbial community of the water was evaluated, and results will be presented. Based on these findings, the probiotic-supplemented diets appeared to enhance tilapia survival after long-term rearing in biofloc culture systems.