The performance of the progeny of eastern oysters Crassostrea virginica from Louisiana selected for resistance to dermo, caused by Perkinsus marinus (referred to as 'OBOY') and of wild oysters collected from Louisiana (Calcasieu Lake) and Alabama (Cedar Point, Perdido Pass), USA, estuaries was compared for their potential use in aquaculture. Seed oysters from each stock were deployed in September 2011 at 2 dermo-endemic sites, Dauphin Island and Sandy Bay, Alabama, using an adjustable longline system, and their survival and shell heights were monitored bimonthly. P. marinus infection intensity and condition index were measured at deployment and in March, July and September 2012. The OBOY stock showed lower mortality than the unselected stocks (Cedar Point, Perdido Pass, Calcasieu Lake) at Dauphin Island, and both Louisiana stocks had lower mortality than the Alabama stocks at Sandy Bay, a slightly more saline site. Mortality increased in summer, especially between July and September, concomitant with increasing P. marinus infection intensities at the higher temperatures and favorable salinities. At the higher salinity site, both Louisiana stocks had lower P. marinus infection intensities than the Perdido Pass stock, the stock with the highest percentage of oysters with moderate and heavy infection and cumulative mortality. The OBOY stock reached greater mean shell height than Calcasieu Lake and Perdido Pass stocks. Condition index of the oyster stocks decreased by more than half between March and July following expected spawning. Differences in stock performance highlight the importance of stock selection for aquaculture in dermo-endemic estuaries of the northern Gulf of Mexico.
The efficacy of a flow-through depuration system in eliminating the human pathogen Vibrio vulnificus from eastern oysters (Crassostrea virginica) collected from the North Gulf of Mexico coast was evaluated in this study. Depuration experiments were conducted with artificially inoculated oysters using laboratory-grown strains of V. vulnificus as well as with naturally contaminated oysters. Determination of V. vulnificus numbers in oyster tissues was conducted at 0, 1, 2, 3 and 6 days of depuration. Results showed that the depuration of V vulnificus is possible using a flow-through system. Numbers of V. vulnificus in laboratory-inoculated oysters were reduced from >100,000 Most Probable Number (MPN)/g of oyster tissue to 23 MPN/g after six days of depuration. As expected depuration results of naturally contaminated oysters were more variable. Depuration at low temperature (15°C) had very little success in reducing the numbers of V. vulnificus in oyster tissues. On the contrary, when flow rate was increased from 11 L/m to 68 L/m, numbers of V. vulnificus in oysters were reduced from a starting concentration of 110,000 MPN/g to 3 MPN/g in six days. Nevertheless, a high-flow rate was not enough to eliminate V. vulnificus from oysters consistently. Vibrio vulnificus was effectively eliminated from oysters only when incoming water salinity was higher than 30 parts per thousand (ppt). Depuration did not select for pathogenic V. vulnificus strains. Pre-and post depuration V. vulnificus isolates contained similar proportions of the proposed more virulent type.
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