Single strain versus multi-strain probiotics in aquaculture: comparative impacts on gut microbiota and immune responses in fish and shellfish.

Probiotics have gained wide popularity as environmentally sustainable replacement for antibiotics in aquaculture due to their ability to up-regulate the host immune competence and boost disease resistance. However, considerable knowledge is yet to gain regarding differential efficacies and mechanisms of actions of Single-strain vs multi-strain probiotics. In the present review, the differences between the immunomodulatory potentials of Single-strain and multi-strain probiotics in fish and shellfish were thoroughly compared, with focus on immune gene expression of immunity markers and alteration of gut microflora. Single-strain probiotics usually mount a targeted immune response by enhancing the expression of particular immunity parameters, whereas multi-strain probiotics generally interact synergistic to induce more general and enhanced immune response and greater microbial diversity in the gut. Molecular basis and mechanisms underpinning probiotic mediated immunomodulation were also comprehensively documented in this review. Although recent evidence demonstrate that multi-strain probiotics tend to offer a broader and consistent immune defence against pathogens than Single-strain formulations, the efficacy of probiotic supplements is often context-specific, depending on the rearing environmental condition, dosage, strains compatibility etc. The combination of probiotics and biofloc system has been proposed as a promising and eco-friendly technology for the development of the sustainable aquaculture and animal welfare. Finally, existing research gaps and future directions have also been discussed for sustainable aquaculture.