Fish can’t drown the way people do, because they don’t fill lungs with water, but they can suffocate underwater. A fish dies when its gills can’t get enough oxygen: the water is low in dissolved oxygen, the gills are damaged, or water stops flowing over them. Some air-breathing fish also die if kept from the surface.
Last updated: October 18, 2026. Facts checked against the sources listed at the end of this article.
It’s easy to take fish for granted. You forget how impressive it is that they manage to live in a vastly different environment to us.
Thinking about the life of a fish, leads to lots of questions like ‘how do fish mate?’ and ‘do they sleep?’.
Another common question people ask is: “can fish drown?“
Fish need oxygen just like humans do, but because they live in water it doesn’t seem like they’d be able to drown. They’ve adapted gills that let them extract oxygen from the water, so is it possible to drown when they can breathe in water?
This article will investigate the question by looking at important factors like do fish have lungs, how fish breathe, and much more…
1. Do Fish Actually Need Oxygen
Yes, fish need oxygen just as humans do; they simply get it from the water. Instead of taking oxygen from the air like us, they collect dissolved oxygen from the water as they swim.
There’s a lot more oxygen in the air than there is in water. This makes it much easier to get oxygen when living on land, but fish have evolved gills to let them survive in water.
Breathing in water has its problems, the salt levels of water can vary a lot.
- Saltwater fish absorb a large amount of salt while respiring because it’s in the water. Consequently, they need a specialized mechanism to remove excess salt from their body.
- Freshwater fish have the opposite problem. There isn’t much salt in the water, so they need a mechanism to hold on to as much of it as they can.
Fish need oxygen for the same reason as humans. Without it, they’ll struggle to respire, and eventually die.
Oxygen gets combined with other elements to create proteins and even form new cells.
When breaking down food in the body, oxygen is used to convert and store its energy. This energy is used in all active processes within the body.
Fish don’t need quite as much oxygen as us since they’re cold blooded. Warm blooded animals need extra energy to keep the body heated. Fish don’t need this energy, so they can survive with less food and oxygen.
There’s a finite amount of oxygen in a body of water. The larger the body of water, the larger the surface area, and as a result the more oxygen.
In an aquarium this can be a big problem. There’s only a small amount of water, meaning it can quickly run out of oxygen. This is just one reason why tank size is so important.
Aquarists can use plants to introduce some oxygen into the tank as they photosynthesize. Air pumps are useful too as they bring oxygen depleted water up to the surface, forming a small circulation.
2. Do Fish Have Lungs and What Are Labyrinth Organs
Most fish don’t have lungs: they breathe with gills. The exceptions are lungfish, which have lungs, and labyrinth fish such as bettas and gouramis, whose labyrinth organ lets them breathe air at the surface. Most of them that you’ll ever see or hear about will have a set of gills on either side of their body; however this isn’t the case for all fish.
There’s a group of fish called Lungfishes. As you can guess from the name, they have air-breathing lungs as well as gills, although the gills of the four African species are greatly reduced and they are obligate air breathers, according to Wilkie and colleagues (2007).
They’re a small group of six freshwater species which can only be found in Africa, Australia, and South America.
African and South American species can survive their habitat drying out by burrowing into the substrate and entering a state similar to hibernation. They do this by slowing their metabolism down to 1/60th of its normal rate.
There used to be a lot more lungfish and they were spread throughout a larger network of freshwater rivers and lakes. Their numbers have gone down dramatically since Pangaea broke apart.
Lungfish aren’t the only fish that can breathe air, some have a labyrinth organ. This organ act like a lung, letting fish take oxygen from the air rather than water. It’s not usually present in juveniles, they start with gills and later grow labyrinth organs.
Lots of aquarium fish have labyrinth organs, like kissing gouramis and crowntail bettas. Because the labyrinth organ fills most of the gill chamber, their gills are reduced, and some labyrinth species will suffocate if they are prevented from breathing at the surface, according to the Mekong River Commission.
While breathing air is a primitive trait for fish, it can let them live in waters that might not be survivable for any fish respiring in the polluted water.
However in most places the water is perfectly safe, so fish don’t need lungs to breathe air because there’s enough oxygen in the water. Instead, fish have gills, which are perfectly adapted for collecting this oxygen.
3. How Do Fish Breathe and Get Oxygen
Fish breathe by pumping water in through the mouth and out over the gills, where oxygen dissolved in the water passes into the blood.
Before we can answer the question “can fish drown?” we need to look at how fish get oxygen and how they breathe.
Since there’s less oxygen in water compared to air, you need more efficient gas exchange surfaces in order to collect it.
Fish have gills which are able to take in oxygen when it’s just at 5 parts per million (ppm). We breathe air, 21% of which is oxygen (210,000 ppm).
It’s not just about efficiency though, gas exchange surfaces (like gills and lungs) need to be able to deal with the medium you’re in (air or water). For example, our lungs can force air in and out, but we’d suffocate if water filled them.
So how do gills work? Well firstly water needs to pass across them, which is controlled by the operculum (this is a flap of skin that acts as a boundary between the mouth and the gills). The fish lowers the floor of their mouth. This makes the pressure in the mouth lower than the pressure outside, so water is drawn in.
When the fish raises the floor of their mouth, the pressure inside becomes higher than the pressure outside. This forces water out of the mouth through the operculum, and across the gills.
If you keep fish at home you can watch this happen, the operculum moves each breathe. This sight is one of many reasons to keep fish.
To extract oxygen from the water, the gills need a large surface area. A bigger surface means as much water as possible can come into contact with the gills for oxygen to diffuse across.
When the water comes into contact with the gills the oxygen is transferred from the water to the blood via the edge of the lamellae. Each gill arch holds rows of filaments and lamellae, creating a car radiator-like appearance.
Gill anatomy can get a bit confusing, but here’s a basic overview.
4. So, Can Fish Actually Drown
No, not in the strict sense, because fish don’t inhale water into lungs, but they can die from a lack of oxygen underwater, which many people call drowning.
To answer this, we need to think about the definition of the word “drown”. This is a verb defined as when you “die through submersion in and inhalation of water”.
With humans, when water gets in our lungs we can’t get oxygen from it, so we can’t breathe, and therefore, we die.
Fish are physically incapable of drowning because they have gills, not lungs. They can die if there’s not enough dissolved oxygen in the water which would make them suffocate, technically. So, if you’ve wondered can fish drown, the answer is no.
To fully meet the definition, you could argue that the fish has died through “submersion in and inhalation of water” because the water inhaled doesn’t contain enough oxygen. If fish are taken out of water then they’ll die, but not due submersion or inhalation of water, so they’re not drowning.
A more accurate term is probably that fish “suffocate” when there isn’t enough oxygen for them to breathe. To suffocate is defined as to “die from lack of air or inability to breathe”.
5. Fish Suffocation and Drowning
When fish are out of water they still have access to oxygen, and at a much higher concentration. You might wonder what causes them to die if they can still breathe. Well the answer is that they can’t breathe, but it’s not due to a lack of oxygen.
They can’t breathe, because gills aren’t designed to process air, but that doesn’t mean that they can’t do it. The issue is that the air dries them out so that they can no longer function properly.
It’s like being dehydrated. When living in water, a fish’s body stays moist. Since gills are designed to be moist, they don’t work if they dry up out of water.
A fish can suffocate in water as well as out of it. There are lots of ways this could happen. Any damage to the gills is going to reduce their efficiency in collecting oxygen, potentially to a point where they can’t get enough to survive. Damage could come through fighting or disease. Some types of fishing hooks can damage gills, bacteria can block them, and fish that must keep swimming to move water over their gills can suffocate if they get trapped in a net, according to Live Science.
Other causes of suffocation are things that lower the concentration of oxygen in the water. An increase in population size is a good example, more fish are respiring and using up the oxygen.
Oxygen can run out if it’s not being replenished fast enough. In an aquarium this can happen quickly because they usually contain such a small body of water. In a natural environment pollution can lead to a rapid de-oxygenation of water that can’t be replaced fast enough. Warm water holds less dissolved oxygen than cold water, and the U.S. Geological Survey defines water with less than 2 mg/L of oxygen as hypoxic, a level that kills many organisms that cannot escape.
| Cause | Why the fish runs out of oxygen |
|---|---|
| Low dissolved oxygen (warm or still water, overcrowding, algal blooms, pollution) | The water holds too little oxygen for the gills to extract |
| Damaged or diseased gills (fighting, fishing hooks, bacteria) | The gills can no longer take oxygen from the water |
| No water flow over the gills (trapped in a net) | Fish that rely on swimming to move water over their gills suffocate |
| Air-breathing fish kept from the surface (some labyrinth fish, African lungfish) | Their reduced gills cannot supply enough oxygen on their own |
| Out of water | The gills dry out and stop working |
Frequently Asked Questions
Can fish die in water?
Yes. Fish die in water when it holds too little dissolved oxygen, which happens in warm, still or overcrowded water and after algal blooms. The U.S. Geological Survey calls water with less than 2 mg/L of oxygen hypoxic and says hypoxia kills many organisms that can’t escape. A marine biologist at the University of Miami put it simply: a fish can drown.
Can a betta fish drown?
A betta can suffocate if it can’t reach the surface. Bettas are labyrinth fish, and the Mekong River Commission explains that the labyrinth organ fills most of the gill chamber, so their gills are reduced and some species die if prevented from breathing at the surface. Keep a gap between the water and the lid, and avoid anything that traps a betta below.
Why don’t fish drown?
Fish don’t drown because gills, unlike lungs, are built to take oxygen out of water. A fish pumps water in through its mouth and out over its gills, and oxygen dissolved in the water passes into its blood. As Live Science explains, trouble starts only when the gills are damaged or water can’t move across them.
Will a fish die if it stops swimming?
Many fish won’t, because they can pump water over their gills while resting. But some fish must keep swimming so that water flows past their gills, and if they are trapped, for example in a fishing net, they can suffocate, a marine scientist from Oceana told Live Science.
Do fish suffocate out of water?
Yes. Out of water, a fish’s gills dry out and stop working, so the fish can’t take in oxygen even though air holds far more of it than water does. That is suffocation rather than drowning, and it is why a fish dies quickly if it jumps out of its tank.
6. Summary
If we’re being critical then fish can’t really drown; but taking a fish out of water is similar to putting a human in it.
In both cases the subject can’t breathe in the new environment. Gills and lungs are designed for use in water or air, and they’re much more efficient in their natural habitat than the other.
By considering the word “drown” you realize that fish don’t die through the inhalation of water. So while fish can’t drown, they can go through a similar experience when out of water or oxygen.
Do you have any thoughts on the question? Can fish drown? Let us know your thoughts in the comments section below…
Sources
- Live Science: Can fish and other marine animals drown? (June 2021; gill damage from hooks and disease, fish that must swim to breathe, nets). Read October 18, 2026.
- University of Miami News@TheU: “It’s hard to imagine, but a fish can drown” (August 2023; low oxygen and warm water, marine biologists Martin Grosell and Danielle McDonald). Read October 18, 2026.
- U.S. Geological Survey Water Science School: Dissolved oxygen and water (cold water holds more oxygen; under 2 mg/L is hypoxic; algal blooms and decay). Read October 18, 2026.
- Mekong River Commission, Catch and Culture: Labyrinth fish (Anabantoidei) (labyrinth organ, reduced gills, suffocation without surface access). Read October 18, 2026.
- Wilkie and colleagues (2007), Physiological and Biochemical Zoology 80(1): The African lungfish (six lungfish species; African species are obligate air breathers with greatly reduced gills). Read October 18, 2026.
Interesting read, I haven’t even thought about it before. Now I feel sad for the fish that get caught.
I love this because my fish keep dying and only one is left. Now i know they didnt die because they drowned.