EFFECTS OF GEAR TYPE AND SEASON ON Vibrio parahaemolyticus AND V. vulnificus IN FARM-RAISED OYSTERS Crassostrea virginica AFTER ROUTINE HANDLING

Off-bottom oyster aquaculture involves routine handling that exposes oysters to elevated temperatures, causing growth of Vibrio parahaemolyticus (Vp) and V. vulnificus (Vv). Farmers can re-submerse their oysters in the water following routine handling, allowing the elevated levels of Vibrio to return to ambient levels before harvesting for raw consumption. In the past, re-submersion studies have been performed in Alabama during the summer months, when the risk is assumed to be the highest. However, these studies did not cover all periods when a risk may be likely. With re-submersion being a relatively new topic in seafood safety, other factors that may influence recovery times still remain to be investigated. In this study, the questions of gear type and season were tested to examine their effects on re-submersion periods for farm-raised oysters. The two common gear types used for off-bottom aquaculture, floating cages (Oyster Gro) and suspended gear (ALS system), were compared during a spring (early May) and a summer (July) trial. Three treatments were tested for each gear type: 1) tumbled and refrigerated, 2) desiccated, and 3) submersed control. The oysters were removed from the water, the treatments were applied, and then re-submersed at the farm. The recovery of total Vv and Vp, as well as pathogenic Vp (tdh+ and trh+), over a 14-day re-submersion period was examined. The preliminary data show that all Vibrio recovered to ambient levels after 7 days of re-submersion, similar to the results of Grodeska et al. (2017), regardless of gear type.  Although the 7 day re-submersion period was sufficient following a handling treatment, the levels of pathogenic Vp (tdh+ and trh+) were higher during the spring trial, suggesting that the summer months may not have the highest risk of Vibrio illness. These preliminary data indicate that the spring shoulder season could hold the potential for increased risks from Vibrio, and future re-submersion studies should consider both the shoulder seasons as well as the summer season.