Learn How to Identify Fish that's Gone Bad

Eating bad fish can cause food poisoning, so it's important to take extreme precautions when assessing its freshness.
Learn How to Identify Fish that's Gone Bad

Last update: 12 May, 2022

You can vary your protein intake in your diet with some delicious fish, either fresh or frozen. This is why it’s one of our most important foods, thanks to its high nutritional value and for being easy to digest.

There are many ways these days to conserve and transport it with the goal of keeping it fresher for longer. However, sometimes these methods don’t work out.

For that reason, you need to know how to tell if fish has gone bad. Nowadays, differentiating whether a piece is fresh or not is a bit more complicated due to the contemporary sales style: packaging.

Most people want convenience when buying it, and they want it filleted and decapitated. It’s easier to eat these fish without knowing if they’re fresh or not because you normally buy them already frozen.

How to tell if fish has gone bad

Some rotten seafood on ice.

The Food and Agriculture Organization of the United Nations (FAO) considers sensory methods to be one of the most effective ways of recognizing fish that’s gone bad. As it explains it, this involves:

“Evoking, measuring, analyzing and interpreting characteristic reactions of food, perceived through the senses of sight, smell, taste, touch and hearing.”

Thus, you must use your senses to determine certain characteristics of the fish that allow you to know if it isn’t fit for consumption.

  • Smell. Your fish has gone bad if it has a rancid smell; it can occasionally smell like ammonia
  • Skin. It’ll have very soft skin that easily detaches from its scales and meat
  • Eyes. It’ll have sunken eyes, creamy corneas, and gray pupils as if it had cataracts
  • Gills. These are behind their head and are either yellowed or gray
  • Guts. This is the first area affected by spoiling; the fish will be swollen or flaccid and sunken

Fish that’s in good condition

Some fish with ingredients for a meal.

Of course, you can also use your senses to determine the freshness. In this case, the characteristics should correspond to the following:

  • Smell. Fresh fish smells like seaweed, the sea, and conserves all of its nutrients
  • Skin. Fresh it’ll have a vibrant color, with hard and shining scales
  • Eyes. It’ll have protruding eyes, with black pupils that glisten if it’s fresh
  • Gills. The gills will be pink or red, depending on the species, clean, bright, and without slime
  • Guts. The meat is firm and not slippery

Tips to prevent unwanted surprises

A cut fish on a chopping board.

So you don’t have to throw it away, we recommend you cook it within a few days of buying it from the supermarket. If this isn’t possible, you can freeze it. This guarantees that it’ll stay fresh for longer.

In fact, the FAO also notes that freezing prolongs the shelf life of all fish species. In addition, it conserves its properties and prevents the risk of food poisoning. However, you should consider the following:

  • Eating fish that has been in the freezer if you haven’t been at home for a few weeks can be quite risky
  • This is because you don’t know if there were power failures, which would mean that it wasn’t properly frozen

Generally speaking, you shouldn’t leave frozen products out of the freezer for longer than 2 days.

You should never refreeze it. If you discover defrosted fish due to power failure, the safest option is to throw it away.

Refrigeration and freezing prevent the proliferation of more bacteria, but it doesn’t kill them. This allows the decomposing process to accelerate. In summary, if there have been alterations in the preservation techniques, you should throw them away.

Read about the Five Virtues of Fish Oil for Your Health

The moisture content

Some rotten seafood on ice.

When you cook fish, you should look to see whether there is a lot of frozen liquid around it or if it’s dry. If there is liquid present in the bag or container, this means that there could have been some kind of power failure that caused it to defrost.

If everything seems to be OK, you still have to be careful. Defrost it, look at it and smell it. If it has a normal smell and appearance, it’s safe to eat. If not, it’s probably not a good idea.

You shouldn’t eat it the same day if it was caught in saltwater. Dry it well and first put it in the refrigerator.

Finally, you’ll know if it’s fresh or not once you take that first bite. If it doesn’t taste sour or acidic then it’s OK. Your taste buds will know if something isn’t right. You can go ahead and eat it if all of these conditions are met!

  • Evaluación de la calidad del pescado. (s.f.). En Organización de las Naciones Unidas para la Alimentación y la Agricultura (FAO). Recuperado el 16 de diciembre de 2017 de http://www.fao.org/3/V7180S/v7180s09.htm
  • Enfermedades comunes transmitidas a través de los alimentos, causadas por bacterias. Cliver. 1993.
  • Enfriamiento o congelación del pescado. (s.f.). En Organización de las Naciones Unidas para la Alimentación y la Agricultura (FAO). Recuperado el 16 de diciembre de 2017 de http://www.fao.org/3/y5013s/y5013s03.htm