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Oyster disease misidentified


January 27, 2015
By Ruby Gonzalez

A small group of scientists studying Vibrio infections in American shellfish hatcheries believe that the pathogen has been wrongly identified at some hatcheries on the US west coast that have experienced losses. For some time hatchery operators in Washington state have believed that V. tubiashii was responsible for the deaths of stressed oysters at their sites.

         However, Vibrio expert Dr. Gary Richards from Delaware, and some of his colleagues, have recently published a paper suggesting that both V. tubiashii and the genetically similar V. coralliilyticus can kill both Eastern oysters (Crassostrea virginica) and Pacific oysters (C. gigas) in hatcheries when they’re at their most vulnerable larval stages.

         Hitherto it was V. tubiashii that the oyster industry had associated with hatchery losses that sometimes caused serious shortages of seed oysters. However, Richards and his colleagues say that: “Several strains of V. coralliilyticus, such as ATCC 19105 and Pacific isolates RE22 and RE98, had been misidentified as V. tubiashii until recently.”

         Richards team described a study that found strains RE98 and RE22 were the most virulent. The same study also showed that V. coralliilyticus causes mortality in Eastern oyster larvae. The data “suggest that V. coralliilyticus has been a more significant pathogen for larval bivalve shellfish than V. tubiashii, particularly on the US West Coast, contributing to substantial hatchery-associated morbidity and mortality in recent years.”

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         Richards works for the U.S. Department of Agriculture’s Agricultural Research Service in Dover, Delaware.

         Taylor Shellfish’s Bill Dewey told Hatchery International that he’s still not sure that the findings call for any change in production techniques at the hatchery. He said he’ll have to look further into that. He also said that while Vibrio has been known to kill oysters in hatcheries, that usually occurred when they were still larvae, weakened by the struggle against ocean acidification, which inhibits new shell growth, and metamorphosis prior to setting. Hatchery operators had found that larvae that were strong and healthy were not noticeably affected in any noticeable way by Vibrio – of any kind.

—Quentin Dodd


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