How to know if fish is spoiled or not? (5 methods)

In this brief guide, we are going to answer the question “how to know if a fish is spoiled”, discuss the different methods of identifying the spoiled fish and the potential side effects of eating spoiled fish.

How to know if fish is spoiled or not?

Spoiled fish forms a thin layer of slime on its upper surface. It gives off a pungent and foul smell that gets stronger as fish ages. Fish changes its light pink color to glossy or milky white which indicates spoilage. If the texture of the fish has turned spongy, mushy, or unusually soft, it has most probably expired. Sometimes discoloration appears on its surface and it also shows brownish spots that means fish is spoiled. 


Many different types of fish are eaten as seafood food in almost every part of the world. Throughout history, fish has been a significant source of protein and other nutrients for people. Fish can be prepared in several different ways. It can be served raw (uncooked) (e.g., sashimi). 

It can be marinated, pickled, or smoked to cure it. 

It can also be baked, fried, grilled, poached, or steam cooked. Many of the preservation techniques utilized in many cultures have now become outdated, yet they are still used for the taste and texture they provide when ingested. 

Nutritional content:

After cereals, fish, and other seafood are the most vital food, providing around 15% of the world’s protein intake. Lean fish muscle has 18–25% protein by weight, which is comparable to beef or poultry but has a lower calorie content. 

Fish is a high-quality, low-fat protein. Fish consumption is a good source of omega-3 fatty acids. These nutrients are necessary for maintaining the health of our hearts and brains. 

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are two omega-3 fatty acids present in fish (docosahexaenoic acid). As our bodies do not synthesize omega-3 fatty acids, we should obtain them from our diet.

Methods to know if fish is spoiled or not:


The outer surface of the fish will grow wetter as it ages and begins to go rotten, finally developing a thin layer of slime. This is an indication that your fish is starting to deteriorate. The sticky wetness on the meat of spoiled fish will feel thick and slippery to the touch.

When you notice the beginnings of a slimy texture on fresh fish, throw it out.

Even after it has started to go bad, cooked fish will not develop a slimy coating.


Fish meat is usually light pink or white, with a thin, clear film of liquid on top. The meat of fresh or chilled fish will take on a glossy, milky look as it ages and begins to spoil. The fish’s milky regions may also take on a blue or greyish hue.

Discolorations appear as the fish ages and begin to go bad. Look over the meat’s surface. If you notice any areas that aren’t the normal pink color of fish, your fish has likely spoiled.

The majority of the discolorations on fish will be black. Small white-ish patches can appear on rotten fish.


Raw or cooked, all fish has a fishy odor. Refrigerated fish that has gone bad, on the other hand, will emit an increasing fishy odor. If you give this pungent fish smell enough time, it will grow into the foul odor of spoiled meat.

The unpleasant fish odor will become stronger as the salmon continues to spoil. It’s advisable to throw out fish as soon as it starts to stink.

Freezer burn: 

If we keep fish in the freezer for even more than 9 months, it may get freezer burn. Look for ice crystalline peaks on the fish’s surface, as well as any discolored regions. Food that has been burned in the freezer should be thrown away.

Food that has been frozen and burnt is still edible and will not make you sick. However, once freezer burn sets in, fish loses most of its flavor and has a powdery texture.


Fish has a firm texture and feels fresh to touch. It has white lines on its surface but if these lines have disappeared or become grey, it probably means that the fish is spoiled and indicates spoilage. 

Other FAQs about Fish which you may be interested in.

Can you eat a jellyfish?

Can you cook fish sticks in the microwave?

How long can cooked fish stay in the fridge?

Shelf life:

The shelf life of fish depends on the types of fish. But usually, most fish spoil within2 to 3 days. Fish expires earlier than other foods. We must place it in the freezer or fridge to keep it safe and edible for a long time. Most frozen fish or shellfish will keep for an endless period, but the taste and texture will deteriorate over time. 

Cooked fish can be frozen for up to three months at 0°F / -17.8°C or less for maximum quality. Shellfish should be consumed within 3 to 12 months after being frozen raw.

Health effects:

Flushing, itching, rash, headache, rapid or irregular heartbeat, dizziness, perspiration, burning of the mouth and throat, diarrhea, nausea, vomiting, and abdominal cramps are common symptoms that appear quickly, generally within an hour of eating spoiled fish.


In this blog, we discussed different methods to know if fish is spoiled or not. We find out that slimy texture discoloration and strong pungent smell make it easy to tell if fish is spoiled or not. 

We also discussed that fish can stay fresh only for a short period for about 2 to 3 months in the freezer. There are many side effects of eating spoiled fish like diarrhea, nausea, vomiting, and abdominal cramps that can be harmful to human health.