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Why Is My Fish’ Mouth Stuck Open?

Although it is common for fish to have their mouth open for extended periods of time when feeding, when trying to attract a mate, and when trying to warn off a potential predator, some fish can develop various conditions that cause them to have their mouth stuck open.

With fish keeping constantly increasing in popularity, we have noticed more and more questions from the fish keeping community recently with some people asking about their fish’ mouth being stuck open.

There are a number of different reasons that your fish can end up with its mouth stuck open with each of them requiring a different treatment to correct the issue.

Sometimes it is a relatively easy fix where as other times you might have to get a special treatment if your fish has its mouth stuck open due to medical issues.

Due to there being so many different problems that can cause the mouth or jaw of your fish to get stuck open, we see a number of slightly different questions about having the fish’ mouth stuck open.

We have decided to cover them all in this article so have decided to add a table of contents below to try and keep our article as easy to navigate as possible for our readers.

Why Is My Fish’ Mouth Stuck Open?

The four most common reasons that a fish may end up with its mouth stuck open is due to injury, oxygen levels being low in its tank, mouth rot or due to having something stuck in its mouth.

All four are about as common as each other with all but an injury being relatively easy to fix in your fish depending on the size of your fish.

If you have aggressive fish in your aquarium then fishing can be common amongst the fish and it can often lead to extended chasing and nipping periods and this can result in one of your fish ending up with an injury on its mouth.

This can end up getting its mouth stuck open due to damage to the ligaments required to close its mouth and unfortunately, this is often a permanent injury that you are unable to treat.

If the oxygen levels in your aquarium are too low then there are a number of different things that you are able to do to boost the oxygen in the tank.

An old trick to quickly and easily boost the oxygen levels in your tank is to simply pour water into the tank from a height that will cause bobbles when it hits the water.

This is only a temporary solution though and you will probably need to pick up a cheap aerator pump to constantly add oxygen to your tanks water.

What Is Mouth Rot In Fish?

Mouth rot in fish can cause a number of problems ranging from the mouth decaying to the mouth being stuck open with most people having to intervene to treat the issue.

Once the mouth rot has been treat in your fish, some fish can make a full recovery and they will then be able to close their mouth but in some situations, their mouth will have issues for the rest of their life and may be stuck open.

Depending on the exact issue, you can usually treat the mouth rot in your fish with something as simple as Pimafix.

You can follow the easy to understand dosing instructions on the side of the product to correctly dose your tank to treat mouth rot in your fish and you will usually see signs of recovery in around four days.

Keep in mind that mouth rot can be contagious in communal tanks so some people do choose to quarantine the fish that they have with mouth rot to prevent the issue from spreading to their other fish and causing problems with all of their mouths.

If you notice the mouth rot in your fish easily enough then you can often treat it quickly before any long term issues take hold in your fish.

Can Fish Get Food Stuck in Their Mouth?

Some fish species are able to end up with food or substrate stuck in their mouth preventing them from being able to close it.

You can usually identify this as the reason that their mouth is stuck open due to being able to see the food or substrate stuck in your fish’s mouth.

Depending on the size of your fish, you may be able to easily get the obstruction out of your wish easily but other times it can be difficult.

Techniques to free the obstruction from the mouth of your fish to allow it to close it range from using tweezers to physically remove it to taking your fish out of the water, holding it upsidedown, and trying to free the object.

Although it sounds easy, it is actually harder than most people initially think with it sometimes taking much longer to free the object than most people think.

Some fish will be able to free the obstruction themselves over the course of a couple of days if you just leave it to do its own thing but this does only tend to be variants of koi or some bottom feeders with larger mouths.

Other fish will almost always need you to intervene in some way to help them get their mouth closed.


That brings our article going over how to help a fish with its mouth stuck open to an end. Although some of the treatments above may sound difficult, they can usually be done at home without the need for specialist equipment. As we mentioned though, if you pet fish is having problems with its mouth being stuck open due to an injury then it is highly likely that it will always have issues with closing its mouth for the rest of its life.