​Bacterial pathogens of shellfish larvae cause mass mortality events worldwide. These mortality events result in unpredictable hatchery supplies of healthy oyster larvae for shellfish farmers. Multiple studies have reported the benefits of additions of probiotics to shellfish larval cultures to reduce pathogen-induced mortalities. Previously, at Oregon State University’s Hatfield Marine Science Center in Newport, Oregon, three marine bacterial isolates were identified to be highly beneficial when added to oyster (Crassostrea gigas) larval cultures. A single dose of the probiotic combination to one-day-old larvae reduced their acute mortality when exposed to the pathogen Vibrio coralliilyticus RE22 and increased larval metamorphosis success compared to controls with no additions of probiotics.
Under defined axenic studies, a small dose of V. coralliilyticus (20 CFU mL-1) resulted in 94% larval mortality compared with 5% mortality in the control without V. coralliilyticus. Application of only 207 CFU mL-1 of the probiotic mix reduced larval mortality to 8% when challenged with 2 × 103 CFU mL-1 V. coralliilyticus. In subsequent testing under poor larval culture conditions, we observed that additions of 105 CFU mL-1 probiotic mix increased larval survival compared with that of control larvae without probiotics and larvae reared under axenic conditions (Figure 1).
This presentation focuses on recent challenges, successes, and insights gained in the development of strategies for the use of our probiotic mixture in a commercial hatchery. We will present findings on the effects of probiotics on larval development and metamorphosis success, survival against pathogen challenges, and probiotic-associated changes in the Vibrio community of larval cultures.