Fish gasping for air at the surface: what to do in the next 10 minutes

Fish gasping for air at the surface is an emergency: they are not getting enough oxygen, either because the water is short of it or because something is stopping their gills from working. Add an airstone or splash the surface right now, then test for ammonia and nitrite and do a water change with conditioner.

The common causes are warm water, a stopped filter or power cut, overstocking, ammonia or nitrite poisoning, chlorine from untreated tap water, and gill parasites. You don't need to know which one yet. The first steps below help with all of them.

How to identify it

Fish hang at the top, mouths at the surface, gulping. Vets call this "piping".
Gill covers move fast or stay flared open.
Fish crowd near the filter outflow or airstone, where oxygen is highest.
Bottom fish such as corydoras and plecos come up or dash to the surface often.
Larger fish are usually affected first in low oxygen.

Not gasping

Some fish breathe air normally. Bettas, gouramis, paradise fish, many catfish (corydoras dart up for a gulp now and then) and loaches gulp at the surface as part of normal life. It becomes a concern when they do it constantly, along with fast gill movement or other fish gasping too.

Clues to the cause

Clue	Likely cause
Hot day, warm room, heater stuck on	Low oxygen from heat: heatwave
Filter or air pump stopped, power cut	Low oxygen: power cut
Worse in early morning, heavily planted or crowded tank	Low oxygen overnight
New tank, new fish, overfeeding, dead fish	Ammonia or nitrite poisoning
Just added untreated tap water or forgot conditioner	Chlorine or chloramine
Only one or two fish, flared gills, scratching, new fish added recently	Gill flukes or other gill disease
Brown gills	Nitrite poisoning

When it's a problem

Early: one fish occasionally at the surface, breathing a bit fast. Check temperature and test water today.

Serious: several fish at the surface, fast gills.

Emergency: most fish gasping, any fish lying on its side, or fish dying. Do everything in the next section now.

What to do right now

The next 10 minutes:

Get air into the water. Add an airstone, point the filter outlet at the surface, or lower the water level a little so the filter splashes. Surface movement is what puts oxygen into water. In a power cut, use a battery air pump, or scoop and pour water back in from a height every few minutes.
Check the filter is running and not clogged. Check the power.
Check the temperature. Warm water holds less oxygen. If it's above about 28–29°C (82–84°F) for tropical fish, turn off the heater and lights, open the lid, and point a fan across the surface. Cool it gradually, about 1°C (2°F) per hour. Don't drop ice straight in.
Test ammonia and nitrite (and chlorine, if you have a test).
Do a 30–50% water change with water treated with a full dose of conditioner and matched to the tank temperature. This helps with ammonia, nitrite and chlorine. If you've just done a water change and suspect chlorine, add another full dose of conditioner now.
Stop feeding for 24 hours. Digesting food uses oxygen, and food waste makes ammonia.

What to do next

Low oxygen

Keep the extra aeration running for several days, or permanently if the tank is crowded. Reduce stocking if needed. Planted tanks use oxygen at night, so run an airstone on a timer during darkness if fish gasp in the morning. In summer, see heatwave.

Ammonia or nitrite

Change water daily, or twice daily, to keep ammonia and nitrite as low as possible. Use a conditioner that says it binds ammonia and nitrite. For nitrite, a measured dose of aquarium salt protects the blood: see nitrite poisoning. Find the cause: an uncycled tank (cycling), overfeeding, a dead fish, or a filter cleaned in tap water.

Chlorine

Extra conditioner and aeration usually fix this within hours. Fish with burned gills may be weak for days; keep the water very clean. See chlorine.

Gill flukes and gill disease

If the water tests fine, the temperature is right, and fish still gasp, especially after adding new fish, suspect gill flukes: tiny worms that damage the gills. You can't see them without a microscope. Fluke treatments (praziquantel is the common active ingredient) usually need repeating, because the eggs survive treatment. See flukes. Gills damaged by ammonia, nitrite, chlorine or bacteria take days to weeks to heal; keep extra aeration going.

Cautions when medicating

Many medicines lower oxygen in the water, so keep aeration running. Remove carbon from the filter while dosing, and finish the course. Be careful with plecos, loaches, scaleless catfish, shrimp, snails and plants, which react badly to many treatments.

Products that help

Air pump, airline and airstone: the fastest fix for low oxygen; every tank should have one ready.
Battery or USB air pump: keeps fish alive during a power cut.
Water conditioner that removes chlorine and chloramine and binds ammonia: for emergency water changes.
Liquid test kit (ammonia, nitrite, nitrate, pH): finds the cause.
Thermometer: shows if heat is the problem.
Small clip-on fan: cools the water by evaporation in a heatwave.
Fluke treatment: for confirmed or strongly suspected gill flukes.

Keep on hand: a spare air pump and airstone, conditioner and a test kit. Gasping often happens at night or on holidays when shops are closed.

How to prevent it

Run an airstone or keep the filter rippling the surface.
Don't overstock.
Always use conditioner in new water.
Cycle new tanks before adding fish, and add fish slowly.
Test water weekly and after any change.
Quarantine new fish for 2–4 weeks.
Check the heater and thermometer daily, especially in summer.

Why it happened

Fish breathe oxygen dissolved in the water through their gills. Gasping means either too little oxygen is dissolved (heat, no surface movement, too many fish, a power cut) or the gills can't take it up (ammonia, nitrite and chlorine damage the gills or blood; parasites clog them). Either way, the fish is suffocating.

When to get help

Get help if fish keep gasping after aeration, a water change and normal test results, or if they keep dying. An aquatic vet can look at a gill sample under a microscope to find parasites or damage.

In the game

Multiple Tank Syndrome doesn't have a gasping card yet.