UNRAVELING THE MECHANISM BEHIND PROBIOTIC BENEFITS IN RECIRCULATING AQUACULTURE SYSTEMS

Increased knowledge of microbial management issues in recirculating aquaculture systems that subject fish larvae to high abundances of opportunistic pathogens has led to a burst in research investigating the effect of beneficial bacteria supplement, or probiotics, on fish growth and survival, particularly at the larval stages. Often, studies identify potential benefits of the probiotic to the system, including measuring increased survival, but few studies have elucidated on the potential mechanism behind this improvement. It is not enough to know that a probiotic is working, but specific reasons for its success should be identified in order to understand how to better improve the effects of the supplement in the system, and to understand how to transfer the technology to other systems and fish species.

This study aimed to compare results from two separate probiotics trials, where probiotic was administered either directly via the rearing water only, or via the rearing water and live feed, versus a control without probiotic treatment. Common snook Centropomus undecimalis were reared to approximately 30 dph using standard protocols. Administration of probiotic generally doubled larval survival (Fig. 1A), and subsequent transport stress tests indicated improved survival in fish having been treated with the probiotic (Fig. 1B). This benefit could not be described by increased larval growth or variations in standard water quality measurements (nitrate, nitrite, ammonia, pH, dissolved oxygen).

Investigations into the microbiota composition of the rearing water and larvae indicated large differences between experimental trials (performed in different years), with no consistent patterns of microbial groups affected by probiotic administration. Water and larval bacterial communities overall were more significantly impacted by trial day than treatment, even when comparing treated tanks and larvae versus the control. This presentation will dive deeper into the bacterial community compositions and predicted functions during these trials, relating differences over time and treatments to potential influences on survival.