Shellfish are nutritious foods that may be enjoyed in a variety of ways. Shellfish can have a pair of shells (bivalve) or a single shell (univalve). However, the main safety concern is associated with shellfish that are filter feeders (e.g., oysters, clams, scallops, mussels and cockles).
Canadians should be aware of some potential food safety issues associated with these foods. Raw bivalve shellfish can carry bacteria, viruses and toxins that can cause foodborne illness. That's why it is important to harvest, store, handle and prepare shellfish appropriately to help prevent illness.
In particular, children, pregnant women, seniors and people with weakened immune systems are more susceptible to foodborne illness and should avoid eating raw or undercooked shellfish. Susceptibility to certain foodborne infections associated with the consumption of raw shellfish may also be increased in individuals where stomach acidity has been reduced (e.g., frequent users of antacids).
Here are some steps that you can take to prevent foodborne illness from bivalve shellfish:
- When buying shellfish, make sure that it is fresh. Fresh oysters, clams, scallops, mussels and cockles should have tightly closed shells or they should close their shells when you tap them.
- Only purchase shellfish from a reputable retailer. A retailer selling raw shellfish should be able to show you a shellfish shipper's tag.
- Refrigerate shellfish immediately after you buy it and keep it cold (below 4°C).
- Do not put live shellfish in a closed container or into fresh water.
- Place the shellfish in an open container or platter that will hold any raw juices that leak out of the food.
- Cover the shells with a damp cloth and place on the lowest shelf of the refrigerator.
- Store shucked (opened) shellfish in a closed container.
- Raw shellfish can be kept refrigerated for a few days, depending on their freshness and quality, and can be stored in the freezer for 2-4 months.
- Shucked oysters should be frozen if you do not eat them within two days.
- Check the packaging on frozen shellfish. Make sure that the packaging is not torn or open and that there is minimal frost or ice crystal formation on the packaging.
- Too much frost could mean that the shellfish has been frozen for a long time or has been thawed and refrozen.
- Place the frozen shellfish in the freezer immediately after you buy it until you are ready to use it.
- You should never defrost shellfish at room temperature.
- You can thaw your shellfish by using any of the following methods:
- Place the shellfish in a clean container or platter that will hold any raw juices that leak out of the food.
- Place this container or platter on the bottom shelf of the refrigerator to prevent contaminating other foods in the refrigerator.
- Cook the shellfish immediately after it has thawed.
- Immersion in cold water
- Method 1: Under cold running drinking water:
- Thoroughly clean and sanitize the sink before thawing the shellfish.
- The shellfish should be wrapped in leak-proof plastic to prevent cross-contamination.
- Run water on the shellfish until it has thawed.
- Method 2: Soak the shellfish in cold drinking water:
- Use a clean container to hold the shellfish.
- Wrap the shellfish in leak-proof plastic to prevent cross-contamination.
- Cover the shellfish with cold water.
- Change the water every 30 minutes.
- Keep doing this until the shellfish is thawed.
- Method 1: Under cold running drinking water:
- Only use this method if you will be cooking the shellfish immediately.
It is important to separate your shellfish from other foods in your grocery cart and in your refrigerator. This is to make sure that you are not cross-contaminating your food.
- Keep your shellfish separate from other foods in the refrigerator at home by storing them in different containers.
- Place shellfish on the bottom shelf of your refrigerator so raw juices won't drip onto other foods.
Remember, to avoid cross-contamination, thoroughly wash your hands carefully with soap and warm water for at least 20 seconds before and after handling raw shellfish. Clean and sanitize all kitchen surfaces and utensils that have come into contact with raw or partially cooked shellfish and its raw juices.
- Shucked oysters (usually sold in tubs) are not meant for raw consumption.
- It is best to cook oysters, clams, scallops, mussels and cockles to minimize the chances of foodborne illness. Guidelines for cooking bivalve shellfish are:
- Boil oysters, clams, scallops, mussels and cockles until the shells open, and then boil for an additional 3-5 minutes. You should also boil or simmer shucked shellfish for at least 3 minutes or until the edges curl.
- Steam for 4-9 minutes and throw out those that did not open.
- Fry for at least 3 minutes at 190°C (375°F).
- Bake for at least 10 minutes at 230°C (450°F).
- Don't use the same plate or utensils for raw and cooked shellfish because cross-contamination can occur. Raw juices can spread bacteria to your safely cooked food and cause foodborne illness.
Seafood Allergies (fish, crustaceans and shellfish)
Seafood is one of the most common food allergens and can cause severe adverse reactions in those who are allergic to these foods.
The Government of Canada has published a series of pamphlets on the most common food allergens, including seafood allergies.
Marine biotoxins are naturally occurring and are produced by microscopic marine algae. These algae are part of the marine food chain, so their toxins can sometimes be found in bivalve shellfish (such as clams, cockles, mussels, oysters and scallops), some other filter feeding shellfish such as whelks and in the digestive glands of crustaceans such as lobster or crab tomalley.
High concentrations of marine biotoxins in shellfish can cause illness in people who eat them. Symptoms can occur in a few minutes or up to 10 hours after eating affected shellfish. Depending on the amount consumed, illness caused by these toxins is often temporary but in the most extreme cases, exposure to marine biotoxins can be fatal.
The federal government has a food safety program in place to monitor shellfish and ensure the safety of shellfish sold in Canada. However, here are some steps that you can take to protect yourself and your family from marine biotoxins:
- Shellfish should be purchased from a reputable retail store or restaurant. A retailer selling raw shellfish should be able to show you a shellfish shipper's tag.
- Only shellfish harvested from "open" harvest areas should be consumed. Shellfish harvesting is only permitted in open areas and such harvest areas are subject to monitoring and testing for marine biotoxins. If in doubt, contact your nearest Fisheries and Oceans Canada (DFO) office for a list of areas that are closed to shellfish harvesting.
- If you have any abnormal symptoms or feel ill after eating shellfish, consult your physician immediately.
- Marine biotoxins can also be present in seafood available in other countries. Tourists should be cautious when consuming seafood, including shellfish, abroad.
What the Government of Canada does to keep our food supply safe
The Government of Canada is committed to food safety.
Health Canada establishes regulations and standards relating to the safety and nutritional quality of foods sold in Canada. Through inspection and enforcement activities, the Canadian Food Inspection Agency verifies that food sold in Canada meets Health Canada's requirements.
For more information
- Food Allergies
- Food Allergies - It's Your Health
- In Your Kitchen: Safety Tips
- Recalls and advisories
- Report an Unsafe Product
- Allergy and Asthma Information Association
- Allergy Safe Communities
- Anaphylaxis Canada
- Association Québécoise des Allergies Alimentaires
- Be Food Safe
- Canadian Partnership for Consumer Food Safety Education
- Food Recalls and Allergy Alerts
- Food Safety Facts on Paralytic Shellfish Poisoning
- Food Safety Portal - Canadian Partnership for Consumer Food Safety Education
- How to Report a Potential Food Safety Incident
- Lunch to Go! Food Safety Tips - Preventing foodborne illness
Advisories and Warnings
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