Probiotics impact resistance to Streptococcus iniae in Nile tilapia (Oreochromis niloticus) reared in biofloc systems

Authors: PADENIYA, UTHPALA - Auburn University; DAVIS, D. ALLEN - Auburn University; LILES, MARK - Auburn University; LAFRENTZ, STACEY - Auburn University; Lafrentz, Benjamin; Shoemaker, Craig; Beck, Benjamin; WELLS, DANIEL - Auburn University; BRUCE, TIMOTHY - Auburn University

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2023
Publication Date: 9/13/2023
Citation: Padeniya, U., Davis, D., Liles, M.R., Lafrentz, S.A., Lafrentz, B.R., Shoemaker, C.A., Beck, B.H., Wells, D.E., Bruce, T.J. 2023. Probiotics impact resistance to Streptococcus iniae in Nile tilapia (Oreochromis niloticus) reared in biofloc systems. Journal of Fish Diseases. 46:1137-1149. https://doi.org/10.1111/jfd.13833.
DOI: https://doi.org/10.1111/jfd.13833

Interpretive Summary: Biofloc systems are environmentally friendly aquaculture systems that utilize recycled nutrients and organic matter for production and are commonly used for tilapia aquaculture. Beneficial microorganisms in biofloc systems produce bioactive metabolites that may deter the growth of pathogenic microbes. Little research has been conducted to evaluate the use of probiotics, beneficial bacteria provided to animals to enhance disease resistance, in tilapia raised in biofloc systems. The present study evaluated two probiotics (B. velezensis AP193 and BiOWiSH FeedBuilder Syn 3) for use in Nile tilapia raised in a biofloc system. Tilapia were randomly assigned three diets: a commercial control diet or a commercial diet top-coated with either AP193 or BiOWiSH FeedBuilder Syn3 and fed for 16 weeks. At 14 and 16 weeks, the fish were challenged with Streptococcus iniae, a causative agent of streptococcosis, to determine if feeding probiotics alters disease resistance. Additionally, different immune system parameters were examined to determine the effect of feeding probiotics on the immune system. In both bacterial challenges, tilapia fed both probiotics exhibited significantly reduced mortality compared to fish fed the control diet. Although there were some strong trends, probiotic applications did not result in any significant immune system changes related to diet during feeding and following exposure to S. iniae. Study findings demonstrate the applicability of probiotics as a dietary supplement for tilapia reared in biofloc systems.

Technical Abstract: 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. Biofloc technology could be useful for further integration, such as adding probiotics to manipulate the microbial community and its interactions within biofloc systems. The present study evaluated two Bacillus sp. 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 percent mortality, lysozyme activity, and expression of 4 genes (il-1ß, il6, il8, and tnfa) from the spleen were measured. In both challenges, the mortalities of the control group were significantly higher (P < 0.05) than in the probiotic diets. Although there were some strong trends, probiotic applications did not result in any 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 tnfa 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.