Shellfish contamination in the Pacific Region

Photo: Noctiluca scintillans, a non-PSP causing algae bloom

Photo of Noctiluca scintillans, a non-PSP causing algae bloom taken from Ladysmith Harbour.

Always check for both bivalve shellfish biotoxins (PSP/Red Tide, ASP, DSP) and sanitary contamination closures if you plan on harvesting and consuming any shellfish.

Paralytic shellfish poison (PSP, also known as red tide), Amnesic shellfish poison (ASP) and Diarrhetic shellfish poison (DSP) 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.

Attention:

Cooking does not destroy the paralytic shellfish toxin.

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. 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.

Eating shellfish with high levels of certain toxins can lead to serious or potentially fatal illnesses such as: Paralytic Shellfish Poisoning (PSP) (commonly known as Red Tide), Amnesic Shellfish Poisoning (ASP) and Diarrhetic Shellfish Poisoning (DSP). Cooking bivalve shellfish does not destroy the toxins that cause illnesses such as PSP, ASP, DSP. Cooked shellfish can still be toxic.

Vibrio parahaemolyticus (Vp), 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. Vibrio parahaemolyticus can be present in bivalve shellfish in harvest areas that are open and approved for shellfish harvesting.  When people consume raw or undercooked bivalve molluscan shellfish, especially oysters, they could be susceptible to infection by Vibrio parahaemolyticus. More information

Related Sites

Contacts

For more information about Shellfish Closures, please contact :

Phone: 250-756-7327
Fax:250-756-7162

Shellfish biologist
DFO South Coast Division
Nanaimo, BC V9T 1K3

Phone: 250-339-3799
Fax: 250-339-4612

Resource Management
DFO South Coast Division
148 Port Augusta St.
Comox, BC V9M 3N6

Shellfish Toxin Updates

Toll free: 1-866-431-FISH
(1-866-431-3474)

Recorded information

or visit your local DFO Office.