Reducing neurotoxic shellfish poison (NSP) in Pacific oysters (Crassostrea gigas) to levels below 20 mouse units center dot 100 G(-1)

摘要

Pacific oysters previously exposed to the algae Karenia breve, which produces neurotoxic shellfish poisoning (NSP), were held in experimental depuration tanks for up to 5 days prior to determination of their NSP levels by mouse bioassay. Although deputation reduced NSP levels in the oysters to around the regulatory limit (20 mouse units - 100 g(-1)), levels below the regulatory limit could not be assured at temperatures of 15degreesC and 20degreesC and salinities of 24parts per thousand and 34parts per thousand with the standard bioassay used. Detoxification appeared less effective at 12degreesC. The use of an in-line filter to remove free algae or ozone to eliminate algae and toxins did not enhance detoxification. Use of a biological filter at 12degreesC in the tanks, or feeding the oysters with Isochrysus galbana also did not assure NSP levels below the regulatory limit. Examination of NSP distribution in the shellfish tissues revealed that during depuration, the percentage of this lipid soluble toxin associated with the organs of the digestive system (gills and digestive viscera) decreased while levels increased in high lipid tissues, such as the gonads. We postulate that NSP is difficult to eliminate from oysters because it is incorporated into the lipid stores of the animal.