Evaluation of the Efficacy of Candidate Probiotics for Disease Prevention in Shellfish Hatcheries

Abstract

In the United States of America, oyster production is an important component of the seafood economy in many communities in coastal states. The severe impact of disease outbreaks and mass mortality of oyster larvae in hatcheries impacts production, since the oyster industry is largely dependent on hatchery and nursery production. The use of probiotics has been proposed as a potential preventative measure to limit the impact of bacterial diseases in shellfish hatcheries. In previous laboratory studies, the probiotic bacteria Phaeobacter inhibens S4 and Bacillus pumillus RI06-95 improved the survival of eastern oyster (Crassostrea virginica) larvae against the pathogens Vibrio tubiashii RE22 (now V. coralliilyticus) and Roseovarius crassostreae CV919-312T (now Alliroseovarius crassostreae). The aim of this study is to evaluate the efficacy of candidate probiotics P. inhibens S4 and B. pumillus RI06-95 for disease prevention in shellfish hatcheries. Chapter 1 provides an overview of bacterial disease in marine bivalves and the use of probiotics for disease prevention in bivalve hatcheries. Chapter 2 describes that the daily application of P. inhibens S4 and B. pumillus RI06-95 mixed with algal feed to culture tanks in the hatchery increased survival of oyster larvae to experimental challenge with V. coralliilyticus RE22. The levels of total Vibrios in water and surfaces of tanks treated with probiotics were significantly decreased (p < 0.05) compared to non-treated tanks, whereas there were no significant differences between treatments in levels of Vibrios in oysters. These probiotic strains had no significant impact on oyster larvae growth and survival rate at the hatchery. Chapter 3 evaluates the safety and efficacy of candidate probiotic bacteria strains, P. inhibens S4 and B. pumilus RI06-95, in four bivalve species, including hard clams Mercenaria mercenaria, bay scallops Argopecten irradians, blue mussels Mytilus edulis, and razor clams Ensis directus. Pre-exposure of larvae to 104 CFU/ml of probiotics for 24 h in the laboratory did not protect these bivalve species to challenge with V. coralliilyticus RE22, but pre-exposure to 106 CFU/ml probiotics S4 and a mixture of S4 and RI did confer some protection to bay scallop larvae (RPS; 69 ± 4 %). Daily application of 104 CFU/ml probiotics to tanks with bay scallop larvae at the hatchery offered partial protection against bacterial infection without impacting levels of Vibrios in tank surfaces, water, and larvae. However, although daily probiotic treatment of tanks containing hard clam larvae led to a decrease in the levels of Vibrio sp. in rearing