Do fish float when they die?

In this post, we will answer the question “Do fish float when they die?”. We will also discuss the reasons why dead fish float and how long it takes until a dead fish start floating.

Do fish float when they die?

When a fish dies, it will eventually float, but it will first sink since its body is heavier than water. Once the body has decayed and become buoyant, the remains will begin to rise. 

Furthermore, a dead fish may sink and become entangled in decorations, rocks, or plants in your tank, which may explain why you can’t discover a body; however, some fish jump out of the tank to their death, implying that the remains are outside the tank somewhere. 

If your fish leapt out of the tank, the odour from the rotting dead fish will help you discover it, but you may need to do some recon work to find a body stuck between or under plants and decorations. 

Your fish may occasionally fail to float fully, and you may completely miss it, especially if you have a large, thickly planted aquarium.

When fish die, why do they float? 

Because most fish are slightly denser than water, they descend very instantly when they die. They do, however, become more buoyant with time, similar to a drowned human, as bacterial decomposition creates gases inside the corpse. In most cases, enough gas builds up in the body cavities to cause the corpse to float like a balloon. That isn’t always the case, as I can attest from my fish tank, where they periodically decay on the bottom without being observed.

When a fish dies, how long does it take for it to float? 

To float to the top, a portion of your dead fish must decay. In a cold water tank, it will take between eight and fourteen days, and only a few days in a heated aquarium, depending on the size of your fish. 

A fish that had gas trapped in its body before it died will float faster, whereas a fish that has been lost or is stuck between, below, or inside decorations will not float. 

Since bacteria are responsible for decomposition, I’m guessing that if it also killed your fish, the body would be filled with gases, degrade more quickly, and float more easily.

When your fish died, why didn’t it float? 

There are times when a fish will not float after it has died. The most likely cause is that it has not yet decomposed and will most likely rise to the surface once it does. 

If your fish became trapped in a crevice inside the tank and died, or if it died first and then sank into a thicket or decoration, it may not float even if it decomposes. 

The other possibility is that your fish leapt out of the tank and died as a result of the fall, in which case the body is someplace in your house but not in the tank. 

Even when I don’t have an injured, unwell, or weakfish in the tank, I like to do a fish count at least once a week, based on the conditions above. 

It’s especially useful for shy fish like kuhli loaches and bristlenose plecos, as well as ill and breeding species that can hide for several hours. 

A headcount is also necessary if you have creatures (shrimp, crabs) or snails because they hide a lot, have small bodies, and are prey animals that are frequently killed or devoured by fish.

When a fish sinks to the bottom, what does that mean? 

When fish are dead, they will sink to the bottom; but, if they are alive, they are down there for different reasons. Loaches, plecos, catfish, and some cichlids prefer to swim and dwell at the aquarium’s bottom. They’ll lurk in caves, swim among boulders, and sift through the substrate for food. 

Bottom-dwelling fish are accustomed to remaining at the bottom of the aquarium. Even so, if your fish is generally found in the middle or upper levels of the tank and suddenly begins to swim at the bottom, it could be boring, anxious, or unwell. 

Swim bladder illness is a prevalent ailment that causes this behaviour. A fish with a buoyancy problem may swim to the bottom of the tank, float at the surface, float upside down or on its side, and struggle to maintain its usual body position. 

Your fish may swim in a downward corkscrew spiral if they have another whirling sickness, an uncommon ailment with comparable symptoms, albeit they rarely stay at the bottom. If your fish is bored or stressed by its surroundings, it may stay at the bottom of the tank, but it does not stay floating in one position. A stressed fish will surf up and down on the glass, almost as if it is sizing something outside the tank. 

Given all of these possibilities, if your fish is motionless at the bottom of your aquarium, especially if it’s an active species, examine its gills to see whether it’s breathing. Your fish is most certainly dead if there is no gill movement or body movement normally associated with living animal respiration, and the fins and tail are still. 

Your fish is alive if the gills and body are moving in a breathing action. Even while stress and illness can present themselves in similar ways, the fish may be simply resting or sleeping. To make sure your fish isn’t sick, keep an eye on him for a couple of days and be prepared to take action if you suspect he’s unwell.

How do you know if your fish will die? 

Fish are graceful, low-maintenance pets, but because of their gentle temperament, they may hide ailments quite well. 

They usually hide their illnesses to avoid appearing weak and being picked on by other members. Fish live in a society where the disease is seen as a sign of weakness. 

As a result, as a fish owner, you must keep an eye on all of your fish and master their behaviour to recognize when one is sick. If you’re not attentive, your fish could be on the verge of death by the time you notice it’s sick. 

A sick fish on the verge of death will appear frail and may have difficulty swimming. Your finny may lose appetite and hide behind more plants and decorations than usual.


In this post, we answered the question “Do fish float when they die?”. We also discussed the reasons why dead fish float and how long it takes until a dead fish start floating.

If you have any thoughts or doubts, feel free to drop us a comment below!

Frequently Asked Questions: Do fish float when they die?

When fish die, why do they float? 

You realize your fish is floating in the tank or has leapt out of it. 

How long does it take for a dead fish to float? 

It could take eight to fourteen days in a cold water tank and fewer days in a warm tank, depending on the size of your deceased fish. 

What gives the fish its ability to float? 

Fish have a particular organ that allows them to regulate their swimming depth. The swim bladder, also known as the gas vesicle, is a flexible bag that expands and contracts to change the density of the fish concerning the water. 

When a fish dies, what does it mean? 

Two of the most prevalent causes of fish death in aquariums are ammonia poisoning and drowning due to a lack of oxygen. Keep in mind that the amount of oxygen that can dissolve in aquarium water is regulated to avoid your fish from drowning. 

How do you tell whether a fish is about to die? 

Appetite loss is common. Weakness or boredom are two words that come to mind when I think of you. Floating upside down, floating upside down, or ‘sitting’ on the tank floor are all signs of a loss of balance or buoyancy control (most fish are normally only slightly negatively-buoyant and it takes little effort to maintain position in the water column) Shimmying or erratic/spiral swimming. 

What’s the deal with the fish being upside down? 

If this is not the case with your fish, swimming upside down or sideways could indicate a bacterial infection, parasites, swim bladder dysfunction, or even a lack of fins, which are sometimes lost due to attacks by other fish or illnesses.


Do Fish Always Float to The Top When They Die.

Why do fish float when they die?

Here’s why fish float upside down when they die.

Why Do Dead Fish Float?