Goldfish mouth stuck open, blocked or sore

A goldfish’s mouth does more work than any other part of it. Goldfish are carp, built to find food in mud, and they spend much of the day nosing along the bottom, taking in mouthfuls, sorting them and spitting out what is not food. The mouth is extended forward to do it, pushed into the substrate, rubbed along the glass and knocked against the decor, all day, for years.

So most mouth problems are mechanical: a stone that went in the wrong way, a snout worn on the glass, a lip torn by a net. They look alarming and they are usually simple. One is not: columnaris, a bacterial infection that likes the mouth and can do serious damage in a day. The first job is telling which one you are looking at.

First: can it close its mouth, and can it eat?

Two questions sort almost every case, and they are worth answering before anything else.

Can it close its mouth? Watch it breathe for a minute. A healthy goldfish opens and closes its mouth in a steady rhythm. A fish holding its mouth open at the same gape the whole time has something in the way, or a jaw that is not working.

Can it eat? Drop in a little soft food and watch. A fish that takes it and swallows is in no immediate danger, whatever its lips look like. A fish that comes forward, tries, and fails — or takes food and immediately loses it — has a problem that food will not solve, and the clock is running.

What you see	Most likely	How fast
Mouth held open, jaw working, tries to eat and fails	Something lodged	Watch for a few hours, then help
Mouth held open, nothing visible, after a knock or handling	Jaw injury	A vet, today
Pale, greyish patch on the lips, larger than this morning	Columnaris	Today
Pink, scraped or shortened lips, eating normally	Wear from rubbing	Days: fix the cause
A smooth waxy patch on the lips, in cold months	Carp pox	Watch
Gaping at the surface	Breathing, not the mouth	A water test, now

The last row is there because it catches so many people. A goldfish gaping at the surface is breathing, not suffering from anything in its mouth, and the gasping page is where that belongs.

Something stuck in the mouth

A real mouth emergency in goldfish, and usually a substrate problem.

Goldfish do not chew with their jaws, which have no teeth. They take in a mouthful of whatever is on the bottom, sort it in the mouth and throat, and grind the food with teeth set far back in the pharynx. The anatomy page covers the arrangement. It handles sand, which is spat out, and large stones, which do not fit. Gravel that fits in but cannot be spat out is the risk.

Gravel that fits the mouth can lodge in it

• Sand
• Gravel
• Stones

Sand Too fine to lodge in the mouth or throat.

Gravel If a fish can take a piece in but not spit it out, it can lodge in the mouth or throat. The risky size grows as the fish grows.

Large stones Too big for the mouth, so they cannot lodge. Accents on sand or bare glass, not a floor: waste collects between them.

What to do, in order:

1. Watch for the first few hours. Keepers report that many fish work a stone free on their own, often within minutes. A fish that is still actively trying is usually breathing normally, since water can still pass the open mouth to the gills. The danger is that it cannot eat.
2. Look. Shine a torch through the glass from the side and from the front. Knowing whether it is a stone, a pellet or a growth, and whether it sits in the mouth or further back, is what a vet will ask first.
3. If it is still there after a few hours, or the fish cannot close its mouth, or it has not managed to eat, it needs removing. An aquatic vet can usually do it in minutes, and that is the safest route.

If no vet can be reached within a day or so, do not improvise with tools. No authoritative source describes a home method for freeing a lodged stone, and the rule is the same on every page of this site that touches it: no metal tweezers, no force, and no attempt at all. Keep the water clean, keep ringing round, because many aquatic vets will advise by phone and a general vet can often remove a stone under sedation, and keep the fish quiet. A torn mouth is a far worse problem than a stone that stays for another day while a vet is found. The handling guide covers holding a fish without harming it.

Afterwards, the mouth may be sore for a few days, so feed soft food. And change the substrate: the substrate guide covers the grain sizes that cannot lodge, which are either far too small or far too large. A tank that has lodged one stone has already got the next one on the bottom.

A worn snout and lips

A common mouth appearance, and rarely an emergency.

A goldfish that spends a lot of time nosing along the glass, digging in coarse gravel or bumping the decor wears the lips and the tip of the snout. They turn pink, look slightly raw, and on a fish that has done it for months the lips can look shortened or blunted. The fish eats normally, and nothing spreads.

It heals in clean water over a few weeks, and heals completely if the damage was shallow; the healing page covers the timescales. But it only heals once the cause stops, so the useful question is why the fish is doing it:

• Glass surfing — swimming up and down the glass, nose against it — is often a sign of a tank that is too small, a strong reflection, or a fish begging at the front where it is fed. The tank size guide covers the first.
• Digging in coarse or sharp gravel wears the lips from below, and is another reason to change it.
• Rough decor at snout height. Run a finger over every surface the fish can reach; the decorations guide covers what to look for.

A worn snout that suddenly develops a pale, spreading edge is no longer wear, and belongs in the next section.

Pale, grey or white lips

This is the one that does not wait.

Columnaris favours the mouth, the gills and a saddle-shaped patch across the back. On the lips it shows as a pale or greyish area with a defined edge, often slightly raised at the margin, that grows and can erode the lips away. It moves faster as the water warms and in stressed fish, and it often starts after a change that knocked the tank’s stability.

The practical test is speed. Photograph the mouth now, in good light, and again in a few hours. True fungus on a scraped lip looks much the same. A patch of columnaris will be visibly larger. The fungus and cotton-wool page sets out the differences in full.

If it is spreading, act the same day: test the water, do a water change if anything is out of range, and get a diagnosis. Columnaris responds to treatment, but it needs the right one, and the medication guide explains why working down a shelf of products costs a fish time it does not have. Several fish with pale patches at once is more urgent still.

A mouth that will not close

When nothing is visible and the mouth still will not close, there are three possibilities.

Something lodged out of sight, near the hinge or in the throat. The torch from several angles is worth a second try, and a vet can look properly.

A jaw injury. A collision at speed, a fish that jumped, or rough handling can dislocate or break the jaw, and a stone that stayed lodged for days can leave damage behind. The mouth sits at an unusual angle or will not close, and the fish struggles to feed. This needs a vet, and the first aid page covers what to do in the meantime.

A jaw that was always like that. Some fancy goldfish are born with a jaw that never closes fully or sits slightly crooked. If you have had the fish for a long time, it has always looked this way, and it feeds, then it is a shape, not an illness, and the damaged goldfish page covers keeping a fish like that well.

Lumps on and around the mouth

Growths near the mouth are less common and usually slow.

Carp pox, as keepers use the name, appears as smooth, waxy, off-white patches like drops of candle wax, often on the lips and fins, usually in the cold months, and often fades as the water warms. The virus behind the name is known only in common carp and koi, so on a goldfish it describes the look and not a proven cause; the patches are usually harmless to the fish’s health and need no treatment. Papillomas and, rarely, tumours also grow here. The lumps and growths page covers telling them apart.

What decides whether a growth near the mouth matters is function, not appearance. A lump that does not interfere with feeding or with closing the mouth can be photographed and watched month to month. One that starts to get in the way of either is worth a vet’s opinion, and small external growths can be removed under anaesthetic.

Feeding a fish with a sore mouth

Most fish with a mouth problem can eat, given food that asks less of them.

• Soak pellets until they are soft right through, or use small sinking pellets that need no effort to take in. The pellet guide covers sizes.
• Gel food holds together, stays where it lands and can be cut small; the gel food guide covers making it.
• Blanched, finely chopped vegetables are soft and easy to take.
• Feed where the fish rests, and feed the others first elsewhere, so a sore fish is not also a hungry one.

The feeding a sick goldfish page covers the rest. The line that matters is the same as for any fish: a goldfish that has not managed to take anything in for a day or more, despite trying, needs help rather than different food. The not eating page covers the difference between a fish that will not eat and one that cannot.

Preventing the next one

Almost every mouth problem in goldfish traces back to the tank, which makes them among the most preventable problems there are.

• The substrate. Sand, a bare bottom, or stones far too large to enter the mouth of your largest fish. Nothing in between.
• The decor. Smooth surfaces at snout height, and nothing the fish can wedge its head into.
• The space. A fish with room to swim spends less time pacing the glass.
• The handling. A net that is fine and soft, or better still a container, and as few netting sessions as possible.
• The water. Clean, stable water heals small wounds before anything can take hold of them, and columnaris is far less likely in a tank that is not stressing its fish.