Why is Guppy Fish Fat and Swollen?

Guppies can develop a variety of health problems from a variety of causes. Water temperature fluctuations can affect them just as much as water oxygen levels, improper feeding, disease, and overcrowding.

When that happens, guppies will generally show signs of illness, which may vary depending on the condition.

Bloating can be such a sign, but not always. There are many reasons why your guppies may be bloated, and today we will assess the 3 most common ones.

1. Pregnancy

Female guppies will get pregnant approximately once every 30 days. If you have several males in the tank, you will get more females getting pregnant at once. To minimize the number of pregnant females, you should keep 1 male for every 3 females.

The problem is that, with all your precautions, females can still get pregnant. A female guppy can store the male’s sperm after mating for about 10 months to a year. She can then use the sperm deposits to self-impregnant, practically removing the male from the equation.

This means that even newly purchased guppy females can give birth monthly, despite you not having any males in the tank. It’s one of the main reasons why most guppy owners panic when seeing their guppies swollen and fat for no apparent reason.

Fortunately, there is no reason for concern unless you’re not planning on keeping the fry.

2. Overfeeding and Constipation

Overfeeding is a problem for guppies. Not only it affects them physically but can pollute their environment as well. Overfeeding leads to food residues accumulating on the substrate, decaying, and increasing the ammonia levels in the tank as a result.

It will also constipate the guppies, leading to an inflated belly and visible discomfort. Aside from overfeeding, the lack of dietary fibers is another common cause for constipation in guppies.

3. Dropsy

Dropsy is the result of bacterial infections often resulting from improper tank conditions and dirty water. The disease will attack the victim’s kidneys, causing the fish to retain more water than usual. This can lead to a bloated appearance and will cause a variety of other symptoms.

The bad news is that, once the disease has set in, there is little you can do, since it’s usually deadly.

These are the 3 main causes for bloated guppies, and each requires a different approach.

What Should You Do if Your Guppy is Bloated?

Your actions will depend on the cause of bloating. Let’s see what you should do in each case:

– If Your Guppy is Pregnant

First, you need to establish that the guppy is pregnant. The bloated abdomen is usually a good indicator, but there are others to watch out for as well. These include:

  • Refusal to eat – Many pregnant females will refuse food when the labor sets in. By this time, the female’s belly would have reached its peak. If you didn’t notice the pregnancy by this point, you will now.
  • Swimming in place – Female guppies always tend to swim in place when going into labor. It’s a pretty good indicator of the motive behind its fat belly.
  • The pregnancy spot – This is the most reliable visual indicator you can get. The female will display a dark spot on its belly towards the tail.
  • Shaking – Body shaking is another common sign of labor, signaling that the female is ready to deliver.
  • Looking for a hiding spot – Pregnant females tend to hide or swim near the substrate when the labor begins. They resort to this behavior instinctively, trying to protect their fry from the other fish around them. This is ironic considering that guppy females have no maternal instinct, and many of them even eat their offspring at birth.

Now that you’ve decided that your guppy is pregnant, you should decide what to do next. If you don’t plan on keeping the guppies or only plan on keeping a few, leave the female in the tank. The female will usually deliver between 5 and 200 fry, most of which will fall prey to the other tank occupants.

Guppies will generally eat whatever moves and fits their mouth, whether it’s foreign species or their own. They also don’t shy away from cannibalism and are not famous for their parental instincts.

After the fry are born, you should move the female back into the main tank. If, however, you want to keep the fry, removing the female from the tank is a must. You should place it in a different tank or container with similar water conditions.

Guppy fry have the same water requirements as adults; only their diets will vary a bit. Since they are in full developmental phase, the fry will eat more often than the adults and require a slightly different nutrient intake. Guppy fry need more fat in their meals than adults and a healthy amount of protein and minerals.

You can move the fry into the main tank 2-3 weeks later after they have grown enough for other fish not to see them as prey anymore.

– If Your Guppy is Constipated

Overeating is a problem in guppies since it can affect their health, lead to illness, and even kill them. You can avoid the overeating problem by providing your guppies with as much food as they can eat at once.

Only feed your guppies once or twice per day, change the water weekly, and soak freeze-dried food and pellets before feeding them to your guppies.

If despite all your precautions, your guppy still gets constipated, it’s time for plan B. Don’t feed your guppies for a couple of days. At the end of the fasting, give them crushed cooked peas, which act as a natural laxative for guppies.

If that doesn’t work either, you might have a different problem at hand. I suggest speaking to the vet if the bloated belly doesn’t go away within a couple of days.

– If Your Guppy Has Dropsy

Fortunately, dropsy isn’t that common in guppies, especially if you keep the tank in good condition and ensure the water’s quality. The ideal would be to prevent the condition by cycling the tank properly, changing the water at least once per week, and monitoring the water parameters.

Keeping the temperature, oxygenation level, and ammonia levels in control will keep your guppy population healthy and thriving. But what happens if all these precautions fail and one or more of your guppies show signs of dropsy?

The most common dropsy symptoms include:

  • Swollen belly for no other apparent reason
  • Bulging eyes
  • Swollen and red anus
  • Pale gills and body ulcers
  • The curved spine syndrome
  • Behavioral modifications like unexplained lethargy, swimming near the water’s surface, refusal to eat, or erratic body movements and swimming

When these symptoms occur, and you’ve established that your fish has dropsy, you need to remove it from the tank immediately. Dropsy is generally deadly because once the appearance of symptoms suggests that the disease is already too advanced.

The problem is that dropsy is contagious, so removing the fish from the tank is necessary to avoid the spread.

You can also try treating the fish and hope for the best. This involves removing the sick fish from the tank, placing them into a separate enclosure, and add some Epsom salt into the water. About 2 tablespoons per gallon of water should suffice.

At the same time, change the water in the main tank and add antibiotics to kill all the harmful bacteria responsible for the infection, according to the vet’s recommendations.

Whatever it may be, you need to quarantine the sick fish to prevent the illness from spreading.

Moving forward, you should always change the water occasionally and monitor water parameters to avoid this and more problems.


No matter why your guppies should have an inflated belly, you should always treat the issue with maximum seriousness. Something as trivial as confusing a dropsy victim with a pregnant female can spell disaster for your guppy population.

Another aspect worthy of mentioning is quarantining new guppies. Introducing new fish to the aquarium will always carry some type of risk. You never know whether the new fish are healthy, carry parasites, or have un-symptomatic infections that could spread to the whole tank.

I advise quarantining the new fish for several days before introducing them to the general population.

You should also remember not to overfeed your guppies, clean the tank, and monitor water parameters consistently to avoid bacterial accumulation.

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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