Test of the effects of geography, gear type, and culture techniques on Vibrio risks associated with farm-raised oysters

Abstract

During the off-bottom aquaculture growing process for the eastern oyster, Crassostrea virginica, farmers routinely remove the oysters for tumbling and desiccation. These routine handling practices improve oyster quality but may result in an increased public health risk from the elevated levels of Vibrio vulnificus and V. parahaemolyticus within the oysters. The oysters can be resubmersed in the water, allowing filter feeding to resume and for elevated Vibrio spp. levels to return to background, or ambient, levels normally found in oysters. This study investigated how the Vibrio spp. recovery times after resubmersion were affected by handling type (desiccation, tumbling, refrigeration), gear type (adjustable longline system, OysterGro® system), geography (Alabama, North Carolina), and time of year (May, July). The results indicate that 7 to 14 days of resubmersion is sufficient for the recovery of elevated Vibrio spp. in oysters from both states that were subjected to the same gear and handling types. The recovery times were similar in oysters that were tumbled and oysters that were desiccated, while the recovery times were similar between the gear types when the same handling treatment was applied to the oysters. The tumbled and refrigerated oysters required 14 days or more of resubmersion after handling, so this type of handling would be discouraged as a common industry practice. These data also suggest that the cooler month of May could require a longer resubmersion period than the summer months. Overall, the data can be used to guide public health agencies and inform future studies.