Why Is My Guppy Swollen? (Solved and explained!)

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Guppies have long been a favorite in the fish-keeping hobby. They are easy-going, colorful, and hardy. Their place in the list of ‘Most Popular Fish Ever’ is well deserved.

I have been keeping and writing about guppies for more than 30 years now. Over that time several thousand guppies have passed through my fish room. Needless to say, when you deal with that many fish, you will occasionally get the odd fish that is unwell.

When you have a guppy who is unwell, early diagnosis is essential. If you notice your guppy is swollen, take a moment to work through the list below and follow the suggestion on how to resolve each issue.

Is Your Swollen Guppy A Pregnant Female?

If you are new to guppy keeping, you may not realize how quickly or how often female guppies are pregnant. Female guppies are essentially always pregnant. They can have a batch of fry every 30 to 40 days for the whole of their lives!

How do you know if your female guppy is pregnant?

If you have a tank with male and female guppies, the chances of a female being pregnant are extremely high.

To decide if your female guppy is pregnant or not, take a moment or two to observe her. A female guppy will be swollen in the belly. If she is heavily pregnant, she will have what is known as a gravid spot, which is a dark patch at the rear of her belly, just above the analfin (see image below).

If a female guppy is heavily pregnant her abdomen will be almost square. They really do become ‘boxey’ just before they give birth.

How Long are Female Guppies Pregnant for?

Female guppies are pregnant for around 30 to 35 days. They are essentially continually pregnant for their whole lives.

Female guppies can actually store sperm from a single mating which they can then use to have multiple batches of babies. It is important to be aware that females can store sperm, especially if you hope to breed a specific female to a male.

Constipation In Guppies

If your guppy isn’t swollen because it is pregnant, the next thing to consider is could it be constipated?

There are a number of reasons a guppy can become constipated. These include;

  • Overeating
  • Poor quality food
  • Internal parasites or tapeworms


Guppies are renowned for overeating. They will literally eat until they explode if you let them. If your guppy is constipated due to overeating, it will usually pass within a day or two.

To prevent overeating, only add as much food as your guppy will eat in a couple of minutes. It is better to feed your guppies little and often. I feed my guppies several small meals a day rather than one large meal.

Poor Quality Food

Cheap, poor-quality foods are full of fillers. Fillers in fish food offer the fish no nutritional value whatsoever. Fillers are just added to fish food to bulk them out. Good quality foods such as Bug Bites by Fluval are made with high-quality ingredients and are less likely to cause bloating or constipation.

Much like with overeating, constipation caused by a guppy eating low-quality food should pass within a day or two.

Internal Parasite and Tapeworms

Internal parasites and tapeworms can be a real problem in guppies. Bloating and constipation caused by intestinal parasites have to be treated with medication. A course of treatment like Paracleanse by Fritz will kill the tapeworms and other internal parasites, allowing the guppy to pass them and eliminate their constipation.

I treat all guppies I buy with Paracleanse just to make sure they don’t bring any internal parasites into my aquariums.


Dropsy looks very different from any of the other issues above. A guppy with Dropsy is unmistakable. If you ever see a guppy with Dropsy, you will notice the belly isn’t just swollen, the whole body can swell up. Sometimes the fish can become so swollen the scales actually stick out making the guppy look like a pinecone!

What is Dropsy? Dropsy is a build-up of fluid inside the body cavity or tissues. There are a number of different causes of Dropsy in guppies. These include bacterial infection, liver dysfunction, and internal parasites.

Treatment for Dropsy is difficult unless the underlying cause is known. Standard practice says the guppy should be placed in quarantine whilst the cause of the Dropsy is diagnosed. Unfortunately, the sad reality is, once it becomes clear the fish is suffering from Dropsy, the end result is the fish dies or requires euthanizing.

If you live in Europe, eSHa 2000 is an effective treatment.

I recently wrote an article titled What is Dropsy in Guppies and what can we do to cure it?.

In Conclusion

If you notice your guppy is swollen, don’t panic. Take a few minutes to watch your guppy and see which issues from the list above are most likely to be the cause.

If your guppy is swollen due to illness or disease, identifying the problem and rectifying it quickly can be the difference between your guppy surviving or dying.

About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James

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