DEVELOPMENT AND OPTIMIZATION OF PROBIOTICS FOR BIVALVE SHELLFISH HATCHERIES
The bivalve shellfish industry is an important and rapidly expanding area of world aquaculture production. Nowadays, a variety of approaches are being taken to combat diseases in bivalve aquaculture. The use of probiotics has been suggested as an inexpensive, safe, and effective tool for preventing disease outbreaks in hatcheries. We have evaluated the use of two candidate probiotic bacteria, Phaeobacter gallaeciensis S4 and Bacillus pumilus RI06-95, against disease caused by bacterial pathogens such as Vibrio coralliilyticus RE22 (formerly V. tubiashii) in bivalve hatcheries. In previous research, we have demonstrated that these candidate probiotic strains have antagonistic effects towards V. coralliilyticus in vitro and that pretreatment of oyster larvae with probiotics during laboratory and hatchery trials provide significant protection against challenge with V. coralliilyticus. Targeted gene knock-out experiments demonstrated that both antibiotic production and the ability to form biofilms contribute to the probiotic activity of S4. Further testing in laboratory and hatchery trials demonstrated that these candidate probiotics also protected bay scallops, Argopecten irradians, against V. coralliilyticus challenge, but not hard clams, Mercenaria mercenaria (Table 1). Probiotics alone had no significant impact on larval survival compared to non-treated controls. These results suggest that these probiotics appear to have species-specific protective effects for shellfish larvae, and that the mechanisms of probiotic action are multifactorial. Two methods (granulation and lyophilization) were used to develop stable formulations of dry probiotics for delivery in commercial settings. While a granulated formulation of RI06-95 provided protection to challenge with V. coralliilyticus RE22 in laboratory settings (RPS; 70 ± 1 %), hatchery trials failed to demonstrate consistent levels of protection. Further research is needed to determine mechanism of action in different species and develop effective and simple means of probiotic delivery for commercial use in shellfish hatcheries. This research has been funded by an award from the Northeast Regional Aquaculture Center.