Do Fish Drown? How Fish Suffocate, and How to Revive a Tired One

Do fish drown? Not the way a person does. Drowning means dying because water fills the lungs, and a fish has no lungs; water is where it breathes. But a fish can suffocate, and it happens more often than you might think: when the water runs short of oxygen, when the gills are torn, and when a fish that has to swim to breathe is held still or pulled backward. Below is how each one works, why a hot summer is the dangerous season, and how to revive a tired fish so it swims off instead of sinking.

A liter of water holds about 8 cm³ of oxygen; a liter of air holds 210. A fish lives on one twenty-sixth of what we breathe, and warm water takes part of that away: water at 90 °F (32 °C) holds half the oxygen of water at 32 °F (0 °C).

Do fish drown? No, but they suffocate in three ways

A fish breathes by moving water over its gills. Water goes in the mouth, passes over thousands of thin red flaps called lamellae, and leaves under the gill covers. Blood inside the lamellae flows the opposite way to the water, so a gill pulls more than 80% of the oxygen out of each mouthful (FISHBIO). How fish breathe has the full picture.

Most fish pump that water themselves. A bass under a dock opens and closes its mouth and gill covers like a bellows. Others cannot: tunas, and sharks such as the great white, must swim forward with the mouth open to push water through. Stop them, and they stop breathing.

So a fish suffocates, as Discover Wildlife put it in 2024, when the water has too little oxygen, when the gills are damaged, or when a fish that needs to swim cannot. None is drowning by the dictionary; all three end the same way.

Can a fish drown if you pull it backward?

Gills work in one direction. Water comes in at the mouth and out at the sides. Drag a fish backward and the flow reverses: water pushes in under the gill covers and lifts the lamellae the wrong way. Little oxygen gets across.

You will read that a shark dragged backward behind a boat drowns in minutes. That may well be true for a shark that must swim to breathe, but every version of the claim traces back to fan sites and forums, not to a study. Nobody has published the measurement. Treat it as likely, not proven.

For the angler the lesson is plain: never pull a fish backward to “wake it up.”

Can a fish drown out of water?

A fish in air does not drown. It suffocates, and fast. In water the lamellae float apart. In air they collapse and stick together like wet tissue paper, the breathing surface shrinks to almost nothing, and oxygen uptake stops.

How long before that matters? Rainbow trout chased to exhaustion survived 88% of the time with no air exposure, 62% after 30 seconds in air, and 28% after 60 seconds (Ferguson and Tufts 1992). The 2015 review by Cook, Lennox, Hinch and Cooke, “Fish out of water,” is the source of the rule of thumb every angler should carry: about 10 seconds of air, then back in.

Some fish cheat. A mudskipper can stay out for about three and a half days on wet skin and a mouthful of water. The mangrove rivulus survives around two months in damp logs. The African lungfish seals itself into a mud cocoon and waits out a dry season of up to two years. The “walking catfish lasts 18 hours” figure appears only on blogs; no study backs it.

Why fish die in warm water

Cold water holds more oxygen than warm. At 32 °F (0 °C) fresh water at saturation carries 14.6 mg of oxygen per liter; at 70 °F (21 °C) it is 8.9; at 90 °F (32 °C) it is 7.3 (USGS). At the same time a warm fish needs more, because its body runs faster. Supply falls as demand rises, which is why fish kills come in August, not February.

The University of Miami wrote in 2023 that “a fish can drown,” after the Gulf of Mexico reached 88 °F (31 °C) that August. The thresholds explain it. Warmwater fish such as bass and catfish want more than 5 mg/L, avoid water below 3, and die below 2 (Fondriest, citing EPA criteria). Trout want 6.5 and cannot take less than 4 for long. Carp get by below 1, and pike have been reported surviving 0.1 mg/L for days. Oxygen is lowest just before dawn, after a night in which the plants used oxygen instead of making it. The water temperature guides carry the comfort bands for each species.

Every way a fish suffocates, and what to do about it

How to revive a tired fish: seven steps

1. Land it fast. In the B.A.S.S. research behind AFTCO’s Bass Care 101, a bass fought for one minute survived better than one fought for three.
2. Unhook it in the water. Wet hands, pliers ready. Count the seconds it spends in air and stop at ten.
3. Hold it upright, facing into the current. In a river, point the nose upstream and let the flow do the breathing. In a lake, face it into the wind-driven ripple.
4. Move it forward slowly, never back and forth. Glide it in a slow figure eight so water flows in at the mouth and out at the gills. Sawing it backward reverses the flow and undoes the work.
5. Watch the gill covers. When they beat steadily on their own, and the fish rights itself when you tilt it, it is ready.
6. Let it choose the moment. Loosen your grip and let it swim off. A fish that rolls belly-up gets picked up and held again.
7. In hot water, take longer. Above 80 °F (27 °C) the water holds less oxygen and the fish needs more, so a two-minute revival is normal. If a legal fish still cannot stay upright after several minutes, keep it.

The catch-and-release guide covers hooks, nets and photos in full.

What a fish kill looks like

A fish kill is suffocation on a lake-wide scale. It shows itself at dawn after a hot, windless night: fish of every size and kind hanging at the surface, mouths at the film, gulping the thin oxygen-rich top layer. Because every species dies at once, it is oxygen, not disease. Carp, which tolerate less than 1 mg/L, are often the last left alive.

A fish gulping at the surface is not resting. A sleeping fish settles low against cover with its gill covers beating slowly; a suffocating one hangs at the top and beats them hard. If you see a kill, call your state fish and wildlife agency; most run a hotline for it.

One line to carry to the water: gills work one way, so revive a fish forward, never backward. More answers to the questions kids ask, and what each means for the angler, in fish facts.