Seafood: Shellfish and Finfish


Finfish, shellfish, and other seafoods are very perishable:  both the composition and the source of seafood contribute to this.  Seafood is high in protein and comes from a natural environ­ment - rivers, lakes, streams, oceans -that can be a source of bacteria, viruses and parasites.  Even farm-raised seafood, grown under controlled conditions, may be a source of pathogens or microorgan­isms that can make you sick.  Seafood often shows up on foodborne illness statistics as one of the most likely foods to cause illness.


No matter where your seafood comes from--fresh or salt water, a seafood dealer, grocery store, or, even if you catch it yourself--you should handle it with care.

Some finfish, including grouper, snapper, mahi-mahi and dolphin, maybe the source of a toxin called ciguatera. This toxin is present in tropical reef areas where these fish are harvested. However, a careful fisher­man will not fish from reef areas that are likely to be a source of ciguatera. Using a good seafood dealer with a reputation for quality will help you to avoid this toxin.

Vibrio bacteria species, including Vibrio vulnificus and Vibrio parahaemolyticus, are bacteria that occur naturally in warm coastal areas.  While historically, these bacteria have been associated with southern coastal area, such as the Gulf of Mexico, increasingly they are also being found in the Northeast, including Long Island Sound. The bacteria are found in higher concentrations in the summer months when water gets warmer.  While you may be more familiar with Vibrio and oysters, these bacteria can affect all kinds of seafood, including lobster and finfish. These bacteria can cause serious illness.  In persons with liver disease, cancer, or another immune-compromising condition, Vibrio typically infects the bloodstream, causing a life-threatening illness.  Vibrio bacteria are destroyed by cooking.


Spoilage is caused by bacteria, enzymes and chemical changes in seafood. Spoilage can begin as soon as seafood is harvested. Spoilage organisms are not the same organisms that cause illness. Spoiled fish can smell bad, be slimy or be rancid. All of this makes the seafood unappetizing, but not necessarily unsafe. However, spoilage can be a sign that the seafood has been mishandled or that it is old. Pathogens can multiply quickly in fish that has not been handled carefully.

In certain types of finfish, spoilage can cause changes in the fish that make them unsafe to eat. These fish (tuna, mackerel, bonito, bluefish, dolphin, mahi-mahi), if not handled safely, can develop the scombroid toxin. This toxin causes a reaction that is not unlike an allergic reaction. Symptoms include sweating, a burning-peppery taste around the mouth and throat, a rash, hives and stomach cramps.

That is why it is important to handle seafood carefully as soon as it is caught - fishermen must get it on ice and keep it cold.


Eating raw shellfish such as oysters, clams and mussels may cause illness if the shellfish came from water that was contaminated with bacteria or viruses from human sewage or from Vibrio species.  According to the FDA, people whose immune systems are compromised should not eat raw or partially-cooked shellfish at all.

Raw finfish have the potential to carry parasites such as the roundworm or the tapeworm. While freezing fish to be used in sushi will kill the parasites, it will have no effect on bacteria that may be on the raw fish. They will remain after the fish has thawed. It is recommended that people with com­promised immune systems do not eat raw finfish such as sashimi or sushi.

What about ceviche? Preparing seafood using a technique called ceviche (also called seviche or cebiche) originated in South America. It is gaining popularity in this country. To make ceviche, cubes or very thin slices of raw fish, scallops or shrimp are marinated in citrus juice. The citrus interacts with the proteins in the fish, causing it to become opaque and firm. This makes the fish look like it is cooked—but, it is NOT.  This process does NOT destroy the bacteria, viruses or parasites that cause foodborne illness.  Some chefs will use sushi-grade, previously frozen seafood which will minimize or eliminate the presence of parasites.  However, freezing does not destroy bacteria or viruses.  Therefore, it is recommended that people with compromised immune system do not eat ceviche.  Instead, cook the seafood, then marinate in the same citrus.  You will get the flavor without the risk for illness.


When you go to a seafood market or the fish counter of your super market, look around. Check for overall cleanliness of the store and especially the cleanliness of the equip­ment and staff handling the seafood. Are employees clean? Is their clothing clean? Are they wearing disposable gloves when handling seafood? Do they change gloves after doing non­food tasks and after handling raw seafood? Ask them how they make sure their seafood is fresh.

Select seafood products at the end of the trip to the market. If you are not going straight home, ask that ice be placed around the product in a sepa­rate plastic bag and, if it’s very warm

outside, put the bag in a cooler.

Follow these steps for buying safe SEAFOOD:

  • Buy only from stores that have a good reputation - do not buy from a truck on the street.
  • Buy only fresh seafood that is refrigerated or iced.
  • Don't buy cooked seafood, such as shrimp, crabs or smoked fish, if dis­played in the same case as raw fish. Bacteria from the raw seafood may contaminate the cooked product.
  • Don't buy frozen seafood if the packages are open, torn or crushed on the edges. If you can see the fish, look for signs of frost or ice crystals. This could mean that the fish has either been stored for a long time or thawed and refrozen.
  • Fish should be labeled if it has been "previously frozen." Often swordfish and shrimp are previously frozen. Ask if you are unsure. (Previously frozen fish should be cooked and eaten, or cooked and frozen for later use).
  • If buying clams, mussels or oysters, ask to see the shellfish shippers tag; this shows that the seafood was caught in safe waters.
  • Have the sales person store live shellfish in a paper bag or a plastic bag with holes punched in it. These crea­tures need air to survive. You need to keep them alive until ready to cook.
  • When buying frozen fish, it should be rock solid to the touch when you buy it. There should be no signs of thawing and refreezing (liquid or stains on the outside of the package).

Look for the following when choosing FRESH fish and shellfish:

  • Take a good look at the fish.
    • The eyes should be clear and bulge a little. Only a few fish, such as wall­eye, have    naturally cloudy eyes.
    • Whole fish and fillets should have firm and shiny flesh. Dull flesh may mean the fish is old. Fresh whole fish should also have bright red gills free from slime. If the flesh doesn't spring back when touched, the fish isn't fresh.
    • There should be no darkening around the edges of the fish, or brown or yellowish    discoloration.
  • The fish should smell fresh and mild, not fishy or ammonia-like.
  • Clams, mussels and oysters should be tightly closed. Do not purchase if they are open.
  • Live lobsters should be moving and lively.

If you CATCH and EAT your own fish…

Be sure to check with your state or local officials to see if there are any advisories about fishing areas and about eating fish from certain areas in your state.

  • Put your catch on ice immediately.
  • Kill, bleed, and gut a fish as quickly as possible after landing. Removing the fish's internal organs and gills slows down spoilage and may also prevent parasites from moving into the fish's flesh.
  • If you can't gut the fish immediately, at least bleed it and chill it until you gut it later
  • Cooling fish is critical.  All fish, gutted or not, spoil rapidly if they aren't chilled right away.

When you get the fish home...

Remember that fish and seafood can be contaminated with microorganisms. Keep raw seafood away from ready-to-eat foods. When packaging for stor­age be sure to wash your hands, uten­sils and counter tops before and after handling the raw seafood. Store in containers that protect other foods from dripping liquids. Place seafood on a tray or plate so that liquids cannot drip onto other foods in your refrigerator.

Store the seafood in the coldest part of the refrigerator at a temperature close to 35° F. Fish kept at 40°F will lose quality faster. Store the fish on ice to keep it colder and increase the shelf life.

Wrap finfish in a moisture-proof paper or plastic wrap. Use fresh or defrosted seafood within one or two days. Finfish that will not be used within a day or two can be wrapped in freezer storage materials and frozen. Fish maybe stored in a freezer at 0°F for up to six months.

Live shellfish should be stored in a paper bag or plastic bag with holes punched in it so that the shellfish can breathe. Do not allow shellfish to sit in water for a long period of time. Use live shellfish within 24 hours of purchase.


When handling seafood, learn to pre­vent "cross-contamination." Cross-contamination happens when raw seafood or its juices come in contact with other foods, cooking utensils, counter tops or cutting boards. Wash your hands before preparing seafood, and use clean utensils, counters, plates and cutting boards. After preparing seafood, wash utensils, cutting boards, counters and hands with hot, soapy water.

Cooking safe FINFISH:

Finfish can be baked, broiled, grilled, poached, sauteed (pan-fried), steamed, stir-fried or microwaved. No matter which cooking method you choose, the general rule is to cook fin-fish until it loses its translucent or raw appearance and the meat begins to flake easily when tested with a fork. When using a food thermometer, the fish should reach at least 145°F. When grilling fish, a good rule of thumb is to cook the fish 10 minutes for every inch of thickness.


  • Steam, boil, grill or broil raw shrimp until they turn pink and firm. Boil or steam for three to five minutes for one pound of medium shrimp in the shell. If shrimp are larger or smaller, adjust cooking time as needed. Stop the cooking by placing in ice water, then drain and refrigerate immediately until serving.
  • Clams, mussels and oys­ters (molluscan shellfish) in the shell should be alive until they are cooked. Discard any raw shellfish whose shells are open and that do not otherwise appear to be alive. When cooked, the shells will open. Steam shellfish for four to nine minutes, or boil them for three to five minutes after they open. Shucked shellfish (removed from the shell) become plump and opaque when cooked thoroughly.
  • Boil shucked oysters for three min­utes; fry them in oil at 375°F for 10 minutes; or bake them for 10 minutes at 450°F. The edges of the oysters start to curl when they are done. 
  • Cook scallops until they turn milky white or opaque and firm. Depending on size, scallops take three to four minutes to cook thoroughly. 
  • Lobster should be bright and lively until they are cooked. Do not prepare a lobster that has died. Boil or bake a lobster until it turns bright red.

Remember... people at higher risk of food poisoning should NOT eat raw or undercooked seafood.

Using cooked seafood in a SALAD:

Cool the seafood completely after cooking. Transfer the seafood to a shallow container, and place in the refrigerator immediately. When han­dling the cooked seafood, it is impor­tant to prepare the salad quickly and return to the refrigerator prior to serving. Seafood salads should be used within 48 hours.

Want to read more?

FDA consumer information about seafood safety

Vibrio infections

Seafood Network Information Center, Consumer Seafood Information