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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 12/14/2015 Publication Date: 2/22/2016 Citation: Richards, G.P. 2016. Hatchery mortalities of larval oysters caused by Vibrio tubiashii and Vibrio coralliilyticus. Meeting Abstract. Aquaculture 2016, Las Vegas, NV, February 22-26, 2016, Page 666. Interpretive Summary: Technical Abstract: Hatchery production of bivalve shellfish has been hampered by the occasional presence of opportunistic pathogens, particularly Vibrio coralliilyticus and Vibrio tubiashii. The present study reports the results of several avenues of research to better define these pathogens and the roles they play in eliciting larval oyster mortalities. Many of the outbreaks originally attributed to V. tubiashii were actually determined by DNA sequencing to be from V. coralliilyticus, better known as a coral pathogen. We sequenced a V. tubiashii (ATCC 19109) and showed that it consists of over 5.5 million base pairs on two chromosomes and four plasmids. We also sequenced a highly pathogenic V. coralliilyticus (strain RE98) which has two chromosomes and two plasmids totaling over 6 million base pairs. Some significant differences can be noted between these two pathogens, including the presence of a zinc-metalloprotease gene in V. coralliilyticus which is missing in V. tubiashii. By means of this gene, the presence of V. coralliilyticus can be confirmed by PCR or a novel dipstick assay that is currently under development. The relative lethal doses of V. coralliilyticus and V. tubiashii in larval Eastern oysters (Crassostrea virginica) and Pacific oysters (C. gigas) were identified. The LD50 values, calculated at 6 days post challenge with V. coralliilyticus, ranged from 1.1 × 10e4 to 4.0 × 10e4 cfu/ml seawater. In contrast, the V. tubiashii strains were highly infectious toward Eastern oyster larvae (LD50 = 3.8 × 10e3 to 1.2 × 10e4 cfu/ml) but were noninfectious toward healthy Pacific oyster larvae. Vibrio coralliilyticus has been repeatedly identified as a pathogen of larval Pacific oysters, but the presence of V. coralliilyticus in East Coast hatcheries has not been reported. We identified the first V. coralliilyticus-associated outbreak in an East Coast hatchery and identified high levels of V. coralliilyticus in sick larvae, low levels in seemingly healthy larvae, and low to moderate levels in algal cultures. Compared with larval production levels in 2014, hatchery yields were down in 2015 by 34%. |
