Is My Fish Pregnant, Fat Or Just Bloated?

By Nadine Oraby | 2020 Update

Is your fish looking unusually bigger all of a sudden?

Here is why:

It is highly likely that your fish is either pregnant, fat or just bloated. In order to determine exactly which one of these conditions your fish is facing, you must look out for other symptoms that are distinct to each condition. A pregnant fish may face swimming difficulty, a bloated fish may have pinecone scales. If none of the other symptoms occur, your fish may just be getting fat.

These symptoms, although most common, can sometimes overlap, making it difficult to reach a solid diagnosis. Hence there are several other factors that you need to consider to get to the bottom of this issue.

To make this easy to understand, let’s break them all down individually.

How to tell if your fish is pregnant

Before you even begin to look for pregnancy symptoms, you must first figure out whether your fish is even capable of giving birth or not. There are only a few varieties of fish that give birth to young fish, also called “fry”. These species are known as viviparous or live-bearing species. The most commonly found viviparous fish are guppies, mollies, platies, swordtails, moonfish and four-eyed fish.

Note: These are the only fish that display signs of pregnancy. Oviparous or egg-laying fish do not show any visible signs of pregnancy.

Once you’ve figured out that your fish is live-bearing, you need to find out the gender of your pet.

So, Is your fish a male or female?

In case you don’t know; here’s how you can tell them apart.

Generally male fish are brighter in color with larger, slimmer bodies. They also have a longer anal and dorsal fin. On the other hand, females are dull in color with smaller bodies and a triangular anal fin. Although these are the common differences, it can be hard to tell the gender in some species. You may need to consult an expert in case you’re unable to differentiate yourself.

Once it’s decided that your pet fish is a live-bearing, female you can begin to get excited for possible good news if you observe the following symptoms.

Bulging gravid spot

We’re sure you must have noticed your fish bulging if you suspect it to be pregnant in the first place. But the position of this bulge is what will indicate a possible pregnancy.

Female fish have a black or red spot below her abdomen, this is known as the gravid spot. In a pregnant fish, this spot will grow larger and darker over the course of 20 to 40 days. This is a sign of a fish carrying fertilized eggs. If this spot appears to be square it means that your pet is about to welcome her babies real soon.

Swimming difficulty

Due to their increased weight and pain caused by contractions, pregnant fish may experience decreased mobility. If you notice that your fish isn’t moving around as much and is spending most of its time at the bottom of the aquarium, you may have a pregnant fish on hand.


It is common for a pregnant fish to hide behind the foliage or decorations in the aquarium. If you observe your pet doing so, do not worry, this just means that your fish is looking for a safe place to deliver her babies. This behavior mostly occurs right before the fish is about to go into labor.

Refusal to food

Unlike human beings who crave food during pregnancy, fish refuse to eat at all. Especially when they are close to giving birth.

So, if your pet fish is showing all or most of these symptoms,

Congratulations! You are about to become a grandparent.

To prepare yourself for the upcoming event, check out this video of a guppy fish giving birth to her adorable fry!

But, before you get ahead of yourself,

You must know that many a time what may seem like a pregnant fish may, in fact, be a bloated fish.

How to tell if your fish is bloated

Bloating, better known as Dropsy is a serious health condition that affects aquarium fish. The symptoms of dropsy are somewhat similar to that of pregnancy which is why the two conditions may get mistaken for each other. However, if you carefully consider all of the symptoms you can differentiate between the two.

Common symptoms of dropsy

Swollen abdomen

A swollen abdomen is considered to be a telltale sign of dropsy. This is caused due to kidney failure which ultimately leads to retention of excess water in the body.

But wait,

isn’t that supposed to be a symptom of pregnancy? I’m sure this question must have popped up in your head right now.

And the answer to that is no, not exactly.

During pregnancy, only a part below the abdomen gets enlarged and darker in color. While a fish infected with dropsy experiences swelling in the entire abdominal region without any change in color.

However not all fish experience this particular symptom, which is why you need to watch out for others.

Other symptoms of dropsy

These include:

  • Pinecone scales
  • Extreme lethargy
  • Loss of appetite
  • Bulging of one or both the eyes
  • Red spots on the body
  • Pale appearance
  • White, stringy, long feces
  • Curved spine
  • Swollen and red anus
  • Swimming near the surface of the water
  • Gasping for air 

If your fish is exhibiting most of the symptoms given in the list above it is almost certain that it is infected with dropsy.

So, what do you do about it?

Treatment for dropsy

Unfortunately, the mortality rate for fish suffering from dropsy is very high and there is little that you can do to help save the little fellow. Doctors suggest that you euthanize the affected fish as the infection is likely to spread, putting the lives of other fish in the aquarium in danger.

But hey, don’t lose hope just yet.

If dropsy is diagnosed early on, it can be treated by taking the measures given below.

1. The first thing you need to do as soon as you suspect your fish is suffering from dropsy is to separate it from the aquarium. You will need to place it in another tank, aka the treatment tank.

2. Ensure that the water in the treatment tank is fresh and clean.

3. Now add salt to the water in 1 teaspoon per gallon ratio.

4. Change the water of the treatment tank frequently and add salt in the same ratio, each time.

5. Ensure you feed the fish on time with high quality, fresh food.

7. Keep a close eye on your fish, if the symptoms seem to be going away maintain the routine until they completely vanish. If not, you may need to give the fish some antibiotics. It is recommended that a 10-day course of broad-spectrum antibiotics be given to completely eradicate the infection. However, if you’re unsure, we suggest you seek help from a specialist.

 8. Once the fish is healthy you may relocate it back to the aquarium.

Now, here’s the good part:

Although dropsy is a common health concern in aquarium fish, it is also possible that your fish may just be getting bigger and healthier and you as a worried parent are just paranoid about it having dropsy.

How to tell if your fish is just fat

If your fish seems to be getting bigger in size but is not showing any physical or behavioral changes such as dulled color, reduced activity and food refusal, rest assured! Your fish is doing just fine.

You may continue feeding it according to its regular diet.


Do not give your fish excess food just because it seems to be getting bigger.

Overfeeding can have serious consequences including digestive ones, like constipation. If your fish is refusing to eat all of a sudden, seems swollen and is not passing stool, it is most likely overfed and constipated. Even if the fish seems to be doing alright, excessive feeding is not a great idea.

Think about it:

Excess food means excess poop and excess poop means less oxygen and more ammonia in the water. In short, an incredibly unhealthy environment.

If you notice your fish constantly swimming near the surface and gasping for air, it is a clear indicator that they are not pleased with their living conditions. In this case, you must change the water and provide your fish with good quality, fresh food in appropriate quantities only.

If you think that you need to alter your pet’s diet, we recommend you consult a veterinarian before you do so.

Tumors in fish

Even though an enlargement in the size of the fish is most commonly linked to pregnancy, bloating or just healthy growth, it is also possible that your fish has developed a tumor. Tumours are often misshaped and benign. Although if cancerous, unfortunately, there are very little chances of survival. This is because there are barely any treatment options available.

All in all, if there’s one piece of advice that I can offer fish keepers, it is to keep your aquariums clean! in case you’re a new fish parent, check out this video to learn how to properly clean your fish tank.

Remember, a healthy environment is the key to happy, healthy fish.


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