Why is my Guppy Fish Swollen?

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A swollen abdomen in guppy fish can be a reason for concern, but not always. If you monitor the health of your fish and inspect them every day, you’ll probably notice that something’s wrong with your guppies early on.

But even if you don’t have a daily ritual of checking up on the status of your fish, a swollen guppy is not something you’ll easily miss.

I’ve heard aquarists complain that their guppy was ok the night before, only to appear to have a swollen belly the next day.

Unfortunately, there isn’t a single reason why guppy fish may be swollen, and it can be difficult to tell right away what’s the root cause of the problem.

Because I know it can be alarming to see your guppy fish in such a state, I’m going to go over the potential reasons why this may happen and what you can do about it.

Here are the reasons why you guppy fish can become bloated or have an enlarged abdomen:

Pregnant Female Guppy

A swollen-looking guppy fish is not always a sign of a problem or disease. Sometimes the reason behind an enlarged abdomen is not an illness, but a natural result guppy fish mating.

Guppy fish mate a lot and produce fry quite often if left to their own devices. That’s why it’s recommended to limit the number of males in an aquarium to prevent them from overbreeding.

The recommended male to female ratio is 1:3 and even with these numbers, the chances of your guppy fish becoming pregnant is extremely high.

If you notice that your female guppy fish has an enlarged belly, it’s probably because she’s pregnant and she’s preparing to release the fry.

To determine if that’s really the case, you need to know more about the signs of guppy pregnancy, so you can distinguish it from diseases.

How to Tell if Guppy Fish is Pregnant?

If you’re raising guppy fish in a mixed-gender aquarium, chances are extremely high that your female guppy is pregnant rather than sick.

Still, to know for sure, you should look for the following signs of female guppy pregnancy:

  • Check for the gravid spot (dark spot located just above the anal fin) to see if it’s enlarged and whether it has a darker color;
  • The abdomen of the female guppy should be rounded and enlarged.

These are some of the physical signs of guppy pregnancy, but there are also behavioral signs, which interpreted together with the physical changes can be construed as symptoms of a guppy fish pregnancy. These are:

  • As the female guppy is preparing to give birth, her belly will have an angular shape;
  • She will separate from the rest of the group and hide in a corner of the aquarium or behind plants.

It’s a good idea to watch out for these signs because they’ll help you know when it’s time to separate the female guppy from other fish, so she can give birth in a different tank.

This is necessary if you want the fry to survive because adult fish won’t know the difference between food and fry, and they’ll end up eating the fry.

After the female guppy releases the fry, you can remove her from the breeding tank and return her to the original tank.

Water parameters in the guppy nursery tank should match those of the original tank. Also, guppy fry should be fed more often than adults (at least 5 small feedings a day) and they should be put on a protein-rich diet (baby brine shrimp, daphnia, vinegar eels, etc.).

If you don’t want your fish breeding anymore, you must find ways to control the guppy population in your aquarium and to prevent your guppies from breeding.

How Often can Female Guppy Fish get Pregnant?

If you continue having female and male guppy fish in the same aquarium, you can expect the female guppy to become pregnant as often as every 30-35 days.

Because female guppy fish can get pregnant multiple times from a single fertilization, simply removing her from a mixed-gender aquarium won’t always guarantee that she won’t get pregnant again.

Once fertilization occurs, the gestation period can last 25-35 days, depending on tank conditions and water conditions.

Guppy females can release anywhere between 5-200 fry, therefore, you can easily end up with an aquarium overrun with guppy fry, which can easily cause overcrowding issues in your aquarium.

There are various methods to control guppy population in your aquarium including separating female and male guppies, removing plants and decorations that can serve as cover for fry, and introducing a female betta fish into the aquarium that will feed on the fry.

If you want to save the fry, the fastest way to do that is to set up a breeding box in the aquarium, which can hold the fry until you can move them to their own tank.

You shouldn’t keep the fry in the breeding box for longer than 2 weeks because they’ll stop growing and they can develop deformities.

Constipated Guppy Fish

Another reason why guppy fish may get a swollen abdomen is because of constipation and indigestion, which causes their belly to swell.

Constipation can be life threatening to your guppies; you should take it seriously. Your fish can become less active and may stop eating.

What Causes Constipation in Guppies?

Guppies — just as many other fish — can become constipated because of overeating, which can cause bloating and indigestion.

Lack of dietary fiber in their diet coupled with feeding them foods that can extend in their bellies (e.g. freeze-dried foods, pellets) can make them bloated and constipated.

One way to ease constipation is to refrain from feeding for a couple of days (fasting), then feed them small amounts of cooked peas, which acts as a natural laxative.

Because it’s always better to prevent constipation than to treat it, you should be careful how much and what kind of food you’re giving to your guppies.

Make sure you soak freeze-dried and pellet-like foods in a bit of aquarium water before feeding and offer them only a small amount of food so as not to overfeed them.

Constipation usually clears up in one or two days, but if your fish is still showing symptoms and his belly isn’t subsiding in volume, then the problem may be something even more serious.

Dropsy Disease

Dropsy disease is a life-threatening condition that causes fish to retain water and have a rounded body shape with protruding scales.

Dropsy can be caused by a variety of factors including bacterial infections and precarious water conditions. The infection can attack the kidneys of your fish, causing them to retain water, hence the bloated look.

The outlooks for fish suffering from dropsy disease are bleak and chances of survival once the disease sets in are low.

How to Treat Dropsy?

Treating dropsy is challenging because as soon as signs start to appear, the damage caused by the bacterial infection on the internal organs of the fish is usually irreversible.

Sick fish should immediately be quarantined and placed in a hospital tank. If dropsy is caused by bacterial infection, there is no treatment for dropsy.

In this case, you should euthanize sick fish and dispose of them to stop the spread of the disease to other fish.

If bacterial infection is not present, some aquarists report some success with daily Epsom salt baths (2 tablespoon of Epsom salt per gallon), performing a major water change, and treating the tank with antibiotics.

Dropsy is not a common disease in guppy fish, especially if you have a well-cycled tank that you carefully look after by periodically replacing the water and monitoring water parameters so that they’re at optimal levels.

If water conditions are not to blame and all water parameters are in their ideal range, the bacteria that causes dropsy can be introduced into the aquarium via new fish that are already infected or via life foods.

Normally, guppy fish with a healthy immune system in a well maintained tank are able to fight off disease-causing bacteria.

The disease will usually take a hold of the tank if water conditions are bad and tank maintenance is poor.


A swollen belly is not always a problem, especially if it’s a female guppy that has an enlarged abdomen and there are no other signs of illness.

If there are multiple fish with swollen bellies of both genders, there is a systemic problem and you should evaluate the situation based on other symptoms.

Being careful not to overfeed your guppies and making sure that their water is clean are both important aspects of preventing constipation and diseases in the aquarium.

When introducing new fish to the aquarium, always quarantine them first to see if they’re healthy. Always feed your fish fresh foods and be careful with live foods that may carry diseases.

I hope my article has answered your question on why your guppy fish look swollen and what can you do to prevent or treat fish with a swollen abdomen.

Updated: February 23, 2022
Questions & Answers
  1. Tracy Nilson

    Can you help if I sent you pic of rally really huge guppie could you tell if she was pregnant

      1. Hello,

        Would itI be able to send you a photo to determine if my guppy is pregnant or disease?

        She is swollen, not active much, always try to stay by herself, no eating or only a little bit. She is still swimming around, not much….

        I am very worry. I have 5 Guppies (1 female, 4 male). I didnt know enough before buying them.

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