Pathology associated with summer oyster mortality in North Carolina

Abstract

Expansion of oyster aquaculture industries throughout the southeastern United States has been met with recurring, often catastrophic mortality events, limiting capacity for industry growth. Numerous etiologies have been proposed, including regional extensions of enigmatic mortality episodes that have been observed in triploid oysters in Chesapeake Bay as well as the mid-Atlantic and Gulf of Mexico coasts. To better understand associated pathology and begin to address etiology, we conducted a longitudinal histological survey at a commercial oyster farm in North Carolina that experiences recurring mortality. Our survey was timed with dramatic mortality experienced across North Carolina oyster farms, with farmer-reported mortalities exceeding 90% of near market-sized oysters. Surveyed oysters presented with persistent digestive diverticula pathology in the weeks leading up to and through the mortality event and suggest that mortality was ultimately a result of nutritional deprivation. These observations are inconsistent with pathology associated with recent observations of triploid associated mortality in eastern oysters, however similar diverticula pathology has been observed with summer mortality in Pacific oysters. Expanded research into comparative etiology throughout impacted regions and across oyster species will help address oyster mortality events worldwide. Further efforts for eastern oysters are now being concentrated toward understanding variation in resistance to recurring mortality events across commercially available oyster lines.

Keywords

• Aquaculture
• Digestive diverticula
• Histology
• Oysters
• Pathology
• Summer mortality