Title : Selection for high-efficacy Lactobacillus-based probiotics for use in Oreochromis niloticus aquaculture
Abstract:
The increasing global population, heightened health awareness, and rising demand for food have accelerated the expansion of aquaculture as a vital solution for food security. Oreochromis niloticus (Nile tilapia) is the third most widely farmed fish species worldwide, valued for its adaptability, rapid growth, and exceptional nutritional profile. This species is rich in protein, lipids, vitamins, and minerals, making it an essential component of aquaculture. As part of the "blue revolution," aquaculture plays a significant role in ensuring a sustainable food supply. However, the industry faces substantial challenges due to the emergence of infectious diseases such as streptococcosis, tilapia lake virus disease (TiLVD), and infectious spleen and necrosis virus, which have led to mass mortalities in tilapia farms globally. Despite current disease management strategies, including antibiotics and vaccines, these outbreaks continue to pose a significant threat to the industry.
One promising approach to mitigating disease impact in aquaculture is enhancing tilapia health through immune system modulation. The use of probiotics, prebiotics, and other immunostimulants in fish feed has gained attention as an effective strategy for improving disease resistance, growth performance, and overall health. Probiotics, which are live microbial agents, provide numerous benefits to aquaculture systems, including improved gut health, enhanced immunity, and better water quality management. These microorganisms contribute to the degradation of organic matter and the reduction of toxic waste ions, thereby creating a healthier aquatic environment.
In this study, 52 microbial isolates were screened to assess their resilience under simulated gastrointestinal conditions, particularly acidic pH and bile salt exposure. Nineteen isolates demonstrated significant tolerance, with TP002, TP017, and TP025 exhibiting exceptional growth at pH 2 and 0.5% bile salt concentration. Secondary characterization of these strains focused on enzymatic activity, antibiotic susceptibility, pathogen exclusion, and waste ion reduction potential. Ten (10) isolates displayed high extracellular enzyme production, including amylase, protease, and cellulase activities ranging from 80% to 95% compared to the control. This enzymatic efficiency was further reflected in the varying ability (4%–80%) of probiotic candidates, particularly TP005, TP007, and TP030, to break down tilapia feed.
Despite these promising attributes, all tested isolates exhibited limited pathogen exclusion efficiency (1%– 3%) against common tilapia pathogens such as Aeromonas hydrophila and Pseudomonas fluorescens (p>0.05). Antibiotic resistance profiling indicated that all isolates were resistant to ampicillin, erythromycin, oxytetracycline, and neomycin (p=0.06), suggesting their potential for gut retention. Waste ion reduction analysis revealed phosphate oxidation at 24.15 mg.L-1 (±0.65), ammonium reduction at 1.95 mg.L-1 (±0.04), and nitrate reduction at 1.57 mg.L-1 (±0.22), indicating a positive impact on water quality. Based on these findings, the top-performing strains will be further developed into a probiotic formulation for evaluation in an aquaculture system.
