Shellfish Contamination

Always check for both PSP and Sanitary Contamination Closures if you plan on harvesting and consuming any shellfish.

Vibrio parahaemolyticus, a naturally occurring bacterium found in shellfish, is present in higher concentrations during the summer months when water temperatures rise. As outdoor temperatures increase, so does the risk of illness associated with eating raw or undercooked bivalve shellfish (e.g. oysters, clams, mussels, scallops, and cockles). To reduce the risk of illness, only harvest shellfish at the water’s edge when the tide is going out, refrigerate immediately, and cook thoroughly before consuming. More information

Paralytic shellfish poison (PSP, also known as red tide) and sanitary contamination affect only bivalve molluscs, i.e., shellfish with two shells. Other shellfish, such as shrimp, prawns, etc., and finfish are not affected.

Shellfish and the waters they inhabit are good indicators of the bacteriological health of the marine environment. Fecal coliform bacteria in the water indicate the presence of human or animal wastes and the possible presence of disease-causing organisms. Shellfish growing waters are considered polluted when the fecal coliform densities exceed a median of 14/100 mL (based on 15 data points). By comparison the standard for drinking water is 0 FC/100 mL while swimming water standard is 200 FC/100mL. The stringent standard for shellfish growing water is necessary due to the filter feeding mechanism of bivalve shellfish which can concentrate bacteria.

PSP is caused by a group of related toxins. The best known of these is saxitoxin (SXT). In all, there are a total of 18 to 24 known toxins comprised of the parent compound, STX and its derivatives. The relative abundance of each poison varies with the species and strain of dinoflagellate. While the gonyautoxins (GTX’s) appear to predominate in the Bay of Fundy, saxitoxin tends to be higher in the Gaspe Region of Quebec. Saxitoxin is the dominant toxin in some British Columbia species. Shellfish and crabs are also tested for domoic acid, which is also a marine toxin produced by naturally occurring plankton. Ingestion of sufficient quantities of domoic acid results in amnesic shellfish poisoning or ASP.

COOKING DOES NOT DESTROY THE PARALYTIC SHELLFISH TOXIN.

For more information about Shellfish Closures, contact :

or visit your local DFO Office.

For more information on shellfish safety - Related Sites:

• Canadian Shellfish Sanitation Program (Canadian Food Inspection Agency site)
• BC Center for Disease Control (BCCDC)
  • Fishing and Shellfish Harvesting
  • Shellfish Advice for Consumers
  • Shellfish Safety: Advice for Harvesters