Do Fish Float When They Die? Telling A Dead Fish From A Live One

A fish floating upside down can be frightening for fish keepers. Do fish float when they die? I will answer that question in this article.

Fish float upside down when they die because they have an organ called the swim bladder in their lower region that is filled with air. When they die, the trapped air in their swim bladder makes them float upside down at the water’s surface.

But there is more! Read on to get the full answer to whether fish float when they die, how you can tell a dead fish from a live one, and many other important concerns about dead fish. 

Do Fish Float When They Die? Telling A Dead Fish From A Live One image

Do Fish Float When They Die?

floating fish

Many fish species float when they die, especially fish with a special organ called the swim bladder. When they die, the trapped air in their swim bladder keeps them floating at the water’s surface. 

But many other fish species do not float when they die. Fish in this category usually do not have a swim bladder. Examples include sharks and Manta rays. 

Live fish typically use their fins to maintain their position at a definite depth, float or move from one place to the other in the water. But when they die, they lose their ability to maintain their balance, and usually end up floating upside down. 

However, it is not always the case that when a fish dies, it must float. If the fish had little or no air in its swim bladder at the time of dying, it is highly unlikely that you would find the fish floating. 

It will usually sink to the bottom of the aquarium only to resurface after the decomposition process causes enough gas to be trapped in it to make it float.

How Long Does It Take For A Dead Fish To Float?


Many fish are slightly heavier than the water. Hence, when they die, they will usually sink to the bottom of the water. 

But in a few days, the decomposition process carried out by the bacterial activities in it will cause air to be trapped in it. 

This will make the fish float again. This usually takes a few days, depending on the temperature of the water. It can take as few as 8 days in cold water, and fewer days in warm water.

Why Is My Dead Fish Not Floating?

dead fish sitting at the bottom

“Why is my dead fish not floating?” is one of the common questions hobbyists ask whether they keep fish indoors in an aquarium or out in a pond. 

There are many reasons for this. Here are some likely reasons your dead fish is not floating.

The Initial Death Stage

As mentioned above, if a fish dies with little or no air in its swim bladder, the death does not suddenly make its swim bladder buoyant. The fish will usually sink to the bottom of the aquarium at this initial stage of its death.

But the decomposition process will begin once the fish sinks. After a few days, the decomposition activities carried out by bacteria inside the fish may produce enough trapped gas in the fish to make it float back to the surface of the aquarium.

So if your dead fish is not floating, it probably died with little to no air in its swim bladder. Chances are that it would float ultimately.

Also, it could be the case that during the decomposition stage, one or two tankmates took bites off the part of the dead fish that was supposed to keep the gas trapped.

By biting those parts, the trapped gas that was supposed to make the fish float escapes, which is why your dead fish does not float. 

You will usually find fish like this with missing body parts decaying at the base of the aquarium.

Your Fish May Not be Dead But Just Shocked or Stressed

It is common for fish to get stuck at the bottom of the tank. This is especially the case when they are startled or shocked and begin to swim frantically in the aquarium. 

One of the main reasons for fish swimming frantically is a rapid change in the water parameters, such as temperature. Fish may begin to find a more comfortable area in the aquarium. 

Your fish may be stuck at the bottom if you have a heavily decorated aquarium. It could have its fins locked between decoration pieces or an aquarium accessory.

In these situations, they may occasionally lock their fins to their sides to keep from tiring out from the struggle to free themselves. 

If you notice that your fish is unusually spending too much time at the bottom of the tank and is not making any movements or showing signs of life, check for signs of life. 

The fish may be going through shock or stress from being trapped. Check for movement of gills to be sure that your fish is still alive. 

You can also free your fish from being stuck to reduce your pet’s stress. It would be best to investigate what startled your fish and caused it to get stuck so that you can correct the problem.

How Long Does It Take For A Dead Fish To Decompose?


How long it will take for fish to decompose depends on many factors. But usually, it can take up to 9 days in shallow waters. 

Although bacteria are usually the main decomposing agents, sometimes you may find other fish in the shallow waters taking bites off the dead fish.

In the aquarium, the decomposition usually depends on the temperature of the aquarium water, among many other things. The higher the temperature, the faster the decomposition process. But the lower the temperature, the slower the decomposition process.

In the deep sea, fish decomposition usually takes a longer time. The main reason is that in the deep sea, fish decomposition is usually carried out by bacteria. Fish decomposition in the sea can take up to 72 days or as little as a month.

Do You Perform A Water Change When A Fish Dies?


Performing a water change is important when a fish dies. It is also important to prevent disease or infection from spreading to other fish in the aquarium. 

When a fish dies in your aquarium, you should first carefully examine the fish to determine the cause of death. 

Rotting fins and scales are signs of disease. They can also be caused by improper water parameters that make the fish susceptible to diseases. 

Ragged and tattered fins are evidence of bullying. This is especially true if you keep aggressive fish species with docile ones. You do not have to worry about the spread of any disease.

A bloated fish can be indicative of an internal infection.

Whatever the case, you must perform a water change to prevent the decaying fish corpse from polluting your water parameters and spreading any diseases to other fish in the aquarium.

How Do You Know When A Fish Is Dying?

fish in aquarium

Some hobbyists have experienced strange behaviors that made them think their fish was dead. This is common with many aquarium fish. 

But here are some of the sure signs to tell a dead fish from a live one in case you wonder if your fish is dead.

Pay Attention To Your Fish’s Eyes

Sunken eyes are a clear sign of death. It is dying if your fish has sunken eyes but is not yet dead. 

Cloudy pupils are also a sign of death in many aquarium fish. However, some fish species normally have cloudy eyes every once in a while. These include Scorpion fish, Pufferfish, and Rabbit fish. 

But you want to pay close attention to the fish. If the cloudy eyes persist for several more days, your fish may be dying. You want to contact the vet immediately.

Look For Signs of Struggle

Signs of struggle signify life. If you find your fish at the bottom of the aquarium looking lifeless, try to scoop it with a net.

A dead fish will not attempt to escape the grasp of the net. But a live fish will try to avoid being caught in the net. 

If your fish struggles to avoid being caught in the net by swimming slowly instead of darting as usual, that could mean your fish is sick and probably dying.

But if your fish does not struggle, you can conclude it is dead.

Check For Breathing

Many fish species breathe through their gills. Check the gills for movement if you notice your fish lying dead at the bottom of the tank. 

If you notice the gills moving, that is a sure sign that your fish is still alive. If it is not making any movements, the next best guess would be that it is sick. 

You can inspect the symptoms, such as fin rot or white spots around its eye, to know what sickness it is and how best to restore your pet’s health.

Many other fish species also breathe with their mouths. A good example is the betta fish. They have a labyrinth organ like Lungfish, allowing them to also breathe from their mouth. 

You will usually see bubbles about every 4-5 minutes come out of their mouth. If you keep a betta fish or any other fish that breathes with its mouth, you can pay attention to the bubbles from its mouth to tell if it is still alive. 

If your fish is lying at the tank’s base without bubbles from its mouth, you can be sure it is a dead fish.

Why Is My Fish Alive But Floating?

fish floating in aquarium

Although dead fish float upside down, it is not surprising to find live fish floating upside down sometimes in the aquarium. The commonest explanation for this behavior is swim bladder disease.

Although it is often represented as a disease, it is more of a disorder. The swim bladder in a fish is an organ that helps the fish maintain a particular position in the water and swim higher or lower in the aquarium. It is usually filled with air, which helps the fish maintain buoyancy.

However, fish with swim bladders can suffer from swim bladder disorder. This is a condition where the swim bladder does not function properly for one or several reasons

These reasons include overfeeding, low water temperatures, damaged organs affecting the bladder, parasitic, and bacterial infections, etc.

Symptoms of this disorder include a curved back, swimming sideways or upside down, a bloated belly, floating on top of the tank, sinking to the bottom, and struggling to swim.

If your fish is floating upside down, but it is still alive, the likely reason is that it is suffering from swim bladder disorder.

Some of the ways you can avoid this disorder in your fish are:

  • Raise the temperature slightly higher than normal to aid digestion
  • Feed highly nutritious food and avoid overfeeding
  • Ensure that the tank is as clean as possible

These preventive measures will ensure that your fish does not suffer from this disorder. You want to isolate the fish from the community tank if it stays with other fish.

Although the disorder is not contagious, the isolation will increase your fish’s chance of survival. Put the fish in a tank without any decorations or accessories.

Do Fish Float When They Sleep?


Fish hardly float when they “sleep”. Nocturnal fish like to find dimly lit hiding spots in the aquarium to rest until the lights go off, and they can come out for activities.

Many diurnal fish species like to fix themselves between plants, and other pieces of decorations in the tank as they take a rest through the night.

Many other fish have awkward resting positions. Some like to stay still on the substrate, while others sleep upside down. Examples include the Pufferfish, and Wrasse. 

In the wild, some fish may float while sleeping but often do so while floating vertically. Examples include dolphins, and whales. 

But it is highly unlikely to find fish floating dead as they rest. 


flaoting fish image with 'faq' text

Do Goldfish Float When They Die?

Goldfish floats when it dies but not all the time. If your fish dies with little or no air in its bladder, it is less likely to float initially.

Also, if other fish eat parts of it after sinking, the trapped air from the decomposition that is supposed to make it float will escape. Hence, your dead fish will not float.

Do Betta Fish Float When They Die?

Most Betta fish will usually sink when they die. But it is not in all cases that betta fish sink when they die.

If you see your Betta fish at the bottom of the tank, you want to examine it closely to ensure it is not dead.


Dead fish normally sink when they die, and float back after some time because of the trapped gas from the decomposition process going on in their bodies. 

But not all dead fish float, and the ones that typically float do not always.

If you have a dead fish in your aquarium, many things can go wrong even after expelling the fish. But the tips above on handling the situation can help you avoid spreading diseases, and remove the cause of death to prevent further deaths in your tank.

The discussions about swim bladder disorder and how fish rests can also help put your mind at ease if you find your fish floating upside down or spending too much time at the aquarium base. 

A good read will help you avoid problems, and save you many worries!

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Prathmesh Gawai
He is the main author and editor at And he loves to share helpful information on aquarium and/or fishkeeping hobby. Prathmesh has over five years of aquarium and/or fishkeeping experience. Currently, he has a Betta fish tank. He has written hundreds of articles on various aquarium fish species and on fish tank maintenance over the last five years. Connect with him on YouTube here. Learn more about him here.

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