In this study, the use of Lactobacillus acidophilus as a probiotic for Nile tilapia (Oreochromis niloticus) culture was studied. Fish survival and the expression of some genes involved in the immune response were assessed. Diet supplementation with L. acidophilus for 15 days caused a significant increase in fish survival during a challenge with Aeromonas hydrophila and variations in immune response related to IL-1b and transferrin expression in Nile tilapia spleen and kidney. Moreover, extracellular products (ECPs) of L. acidophilus showed high antibacterial activity against fish pathogens such as A. hydrophila and Streptococcus agalactiae in vitro. It was also observed that viable L. acidophilus was able to disrupt quorum sensing activity in Chromobacterium violaceum.

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Probiotic bacteria are dened as live microorganisms that administered as a diet supplement can cause modications in the microbiota associated with the gastrointestinal tract of the host and generate benecial effects such as an increase in the food intake conversion, disease resistance and water quality. During the last decade, its application in shrimp farming has become frequent since several commercial products designed for this purpose have emerged. At the same time, although there are a number of scientic articles published on the subject, it is evident that there is a lack of studies oriented to understand the probiotics working mechanisms and to establish the protocols for its implementation, taking into account critical factors such as the stage of cultivation, culture density and dosage in relation to the shrimp immune defense mechanisms and presence of potentially pathogenic organisms. This paper aims to review the most prominent publications regarding the use of probiotics in aquaculture, particularly in shrimp farming, since its use seems to be the alternative with better perspectives to the indiscriminate use of antibiotics that cause problems such as the emergence of multi-resistant bacterial strains that could alter the ecosystems near acuaculture sites and even affect consumer health.

Microbiome components and bacterial isolates related to healthy and epitheliocystis states in aquaculture cycles of cobia fish were studied. We detected well-defined 16S rRNA amplicon gene sequence variants showing differential abundance in healthy or diseased cycles. Isolation trials were performed, and experimental tests were used to determine probiotic potential of the bacterial strains obtained from water, tissues or live food used in this aquaculture model. The taxonomic affiliation of these strains was cross-compared against microbiome components, finding that some of them had close or identical affiliation to the abundant types found in healthy cycles. Strains belonging to the groups already identified as predominant by culture-independent means were screened as potential probiotics based on desirable activities such as antagonism and antibiosis against marine pathogenic bacteria, quorum quenching, bile acid resistance, antibiotic sensitivity and enzymatic activities for improved nutrient digestion. We have also found that in the tracking of microbiome composition across different developmental stages of cobia, healthy cycles exhibited a consistent high relative abundance of a Mesobacillus sp., while in the diseased cycle the emergence of a Vibrio sp. was observed. Our study suggests that epithelocystis in cobia is associated with a displacement of a symbiotic microbiome community linked to the increase frequency of Vibrio species.