EFFECTS OF RAPID COOLING OF EASTERN OYSTERS Crassostrea virginica USING AN ONBOARD CHILLING UNIT

Oyster harvesting is a major industry along the Eastern and Gulf coasts. Eastern oysters (Crassostrea virginica) spawn when the waters start to warm. This usually occurs in the Gulf of Mexico between May and October. Triploid oysters were created to capture the market during the spawning months since they have a highly reduced chance of spawning, therefore retaining glycogen stores and continuing to grow. These oysters are being grown in off-bottom cages to better control the growth, health, and shape of the oysters. This culture allows for an easier harvest of the oysters. A major problem arises during the summer and fall when the water becomes warmer and bacteria flourish. The two major bacteria affecting the oyster industry are Vibrio vulnificus and Vibrio parahaemolyticus. These bacteria are the leading causes of seafood-borne illnesses in the United States. The increase of Vibrio vulnificus and Vibrio parahaemolyticus in the warmer waters has led to stricter time/temperature requirements for harvesting oysters. The current regulation requires mandatory refrigeration within 1 hour of harvest for shellstock, which allows the internal meat temperature to reach 55ºF within 6 hours. This time requirement is not plausible for smaller vessels that are not large enough to hold a refrigeration unit. Chilling the oysters using an on-board icing unit has been proposed with further investigation.

Oysters were chilled in an ice-slurry kept at ≤ 4.5ºC for 8 minutes to reduce the temperature of the oysters and slow vibrio growth. A pump was also used to circulate the water to cool the oysters at a faster rate. The oysters were kept in mesh sacks to reduce moisture and prevent gaping. Multiple samples were taken at each transition point for lab testing. The samples were tested using polymerase chain reaction (PCR), which magnified the DNA strands to test for vibrio. The oysters were also tested for gaping after 7 and 14 days in storage. This experiment was conducted in May and July, and will conclude in September 2015. The results will help advance the use of triploid oysters as viable options for restaurants during the spawning of diploid oysters.