Impact of water salinity and types of oysters on depuration for reducing Vibrio parahaemolyticus in Pacific oysters (Crassostrea gigas)

This study investigated effects of water salinity (10, 20, 25 and 30 ppt), oyster types (diploid and triploid) and oyster sizes (extra small and medium) on depuration for reducing Vibrio parahaemolyticus contamination in Pacific oysters (Crassostrea gigas). Oysters were inoculated with a mixed culture of five clinical strains of V. parahaemolyticus to levels of 104−6 MPN/g and depurated in UV-irradiated water in a recirculating system at 12.5 °C for 5 days. Holding oysters (diploid, extra small) in water with a salinity of 10 ppt for 5 days resulted in about 2 log10 MPN/g reductions of V. parahaemolyticus, which were significantly smaller than those (>3.0 log10 MPN/g) observed in water with higher salinities (20–30 ppt). The types (diploid vs triploid) and sizes (extra small vs medium) of oysters appear to have no impact on the efficacy of depuration for reducing V. parahaemolyticus in oysters. However, the efficacy of depuration in reducing V. parahaemolyticus in oysters can be influenced by water salinity. Such a factor needs to be considered when developing a depuration process for eliminating V. parahaemolyticus in oysters.