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How To Know If Seafood Has Gone Bad

Max. D Gray
By Max. D Gray. Updated: January 27, 2021
How To Know If Seafood Has Gone Bad

Seafood is a delicious type of food which scares many budding chefs. While it is delicious and nutritious when cooked properly, many of us don't know how to prepare it. One particular concern is whether or not it is bad. Fish and shellfish often has a strong smell which can be pungent. While it is related to the fact the seafood has come from the sea, the difference between fresh and bad fish can be difficult to discern for the uninitiated.

At oneHOWTO, we explain how to tell if seafood has gone bad. We see what we need to look for with fish and shellfish to know whether it is safe to eat.

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  1. How to tell if fresh fish has gone bad
  2. How to tell if cooked fish has gone bad
  3. How to tell if shrimp is bad
  4. How to tell if mussels have gone bad
  5. How to tell if crab or lobster has gone bad
  6. How to tell if smoked seafood has gone bad

How to tell if fresh fish has gone bad

Fish is best served as fresh as possible. With sushi, the fish isn't even cooked, but if it is fresh and stored correctly, it will taste delicious. If for some reason we are unsure whether the fish is safe to eat, we can use one of the following methods:

  • Best before date: whether cod, salmon or any type of fresh fish, if you buy it from the supermarket, it should come in packaging with a ‘best before’ or ‘sell by’ date. These dates let us know when we can eat the fish. Even if it smells OK, it is best to not eat fish any point after its best before date as it can be spoiled and the bacteria present can cause serious food poisoning.
  • Color: if the color of the fish has turned flat and milky, then it is a likely sign it is off. Although we will need to know what the fish color looks like in the first place, fish which has gone bad will look like it is not fresh. Some fish which looks OK may still be bad, but all fish that looks bad probably will be.
  • Touch: when fish is no longer fresh, it will start to develop a slimy texture. The scales will have a more viscous feel to them, as will the flesh of the fish itself.
  • Smell: as we stated in the introduction, it can be difficult to know how fish should smell. For this reason, you should give the fish a smell when you know it is fresh. Even if it is a strong smell, it should still be pleasant. When fish goes bad, the bacteria will start to decompose it, something which leads to a very unpleasant rotting smell. If you think there might be a smell of bad fish, then it is best to discard it.

To help you become more accustomed to how fish should smell, go to your local fish market. They will have fresh fish out in the air and you can tell what good fresh fish should smell like.

How to tell if cooked fish has gone bad

The way to tell if cooked fish has gone bad is similar to fresh fish, but there are some key exceptions:

  • Best before date: the best before date determines when you need to cook it by. However, if you have cooked the fish, it should last another 5 to 6 days after you cook it, even if this is after the sell by date.
  • Look: when you cook fish, you can see it has gone bad by how it looks, but not as easily as fresh fish. This is because it will change color when cooked. Look our for any signs of mold or bacteria.
  • Smell: whether cooked or fresh, if the fish smells bad, toss it.

You will need to ensure the fish is cooked properly before you store it. If you undercook fish and some of it is still raw, you will not be able to keep it past the best before date. Take a look at our article on how to cook fresh salmon to know more.

How to tell if shrimp is bad

To know the difference between good shrimp and shrimp that has gone bad, we need to know what to look for. We also need to know whether the shrimp has been cooked, is fresh or has been frozen:

  • Fresh shrimp: the best way to entail your shrimp is fresh and delicious is to buy it live. The shrimp will be kept on ice so they should be slow, but still have some movement. As soon as they die, they will start the process of spoiling, so they need to be kept in the proper conditions. If they are not alive, but you buy them fresh from the counter, you will need to check their color, texture and smell. If they smell bad or are slimy, they will be off. Remember that fresh shrimp are not orange like cooked shrimp. They should be grey and almost translucent.
  • Frozen shrimp: frozen shrimp is often fresher than a lot of ‘fresh shrimp’. This is because it is frozen as soon as it is caught, whereas fresh shrimp loses its freshness en route to where it is sold. You need to cook it as soon as it is thawed, otherwise it can start to spoil. Otherwise, check the best before date and they should be fine.
  • Cooked shrimp: cooked shrimp will last less time than most fish. You should throw it away if it has been in the fridge for more than 3 days or if it starts to show signs of spoilage.
How To Know If Seafood Has Gone Bad - How to tell if shrimp is bad

How to tell if mussels have gone bad

These tips to tell how if mussels have gone bad will work for other shellfish such as clams. Also, make sure you remove any dirt or sand from clams and mussels before cooking:

  • Opening: if the mussel shell is fully open, it is likely to have died. We should never eat dead mussels, they need to be fresh or cooked straight from frozen.
  • Tapping: if the shell is open a little, it doesn't mean it is dead. What we need to do is tap it gently on the countertop. If the shell closes, it is alive and can be cooked. If the shell stays open, it is dead and we need to discard it.
  • Broken shells: if the mussel's shell is cracked and/or broken, it is more likely to be dead. It doesn't mean it will be for sure, but it is usually best to discard them just in case.
  • Frozen: frozen mussels can last as much as 12 months in the freezer. We should be careful with seafood which has freezer burn. This will not necessarily be bad, but it won't taste good.

How to tell if crab or lobster has gone bad

Crustaceans such as crab and lobster are also sold alive. Their appearance must be intact and smell pleasant. Telling if crabs and lobster have gone bad is similar to shrimp. Also like shrimp, fresh crab and lobster will be a different color to the cooked version. Lobsters and crabs are often dark blue when fresh, but will turn a bright orange color due to the heat affecting the protein pigments in the shells. This is the same with a lot of seafood.

How To Know If Seafood Has Gone Bad - How to tell if crab or lobster has gone bad

How to tell if smoked seafood has gone bad

Smoking fish is an ancient way to help it keep for long periods of time. It is what many civilizations did before they had refrigeration. However, the science behind whether or not smoked fish is bad is pretty much the same. Check the color to see if it has lost any of its vibrancy, look for any slimy residue on the fish (smoked fish is drier than other types of fish) and check the smell.

The smoky smell won't mask the smell of rotten or spoiled fish. We may, however, need to get in close. As with all seafood, we need to exercise caution. If the fish is past its best before date, has been poorly stored or has the signs of being spoiled fish, we recommend throwing it out.

You can also buy salted cod. We tell you how to prepare this tasty fish in our article on tricks for desalting cod.

If you want to read similar articles to How To Know If Seafood Has Gone Bad, we recommend you visit our Food & drink category.

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1 comment
Just cooked a large amount of dungess crab legs and claws.Bought frozen.They smelled and tasted of ammonia.Thats a sure sign they are bad, correct?
OneHowTo Editor
Hi Theresa,

Ammonia is a sure sign they are bad. They secrete ammonia as waste, so it is possible they were contaminated. If you bought them frozen, then the company providing them should have frozen them fresh. It is possible this hasn't happened. You should speak to them and maybe even report them if you think they are engaging in practices which do not meet local health codes.
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How To Know If Seafood Has Gone Bad