Fat Tetra Fish- Should you Worry?

Tetra fish add variety, beauty, and color to any aquarium. It’s fun and relaxing to see your fish swimming around the tank. Moreover, it’s rewarding to watch them grow into adults. Sometimes you can see a tetra that seems to keep growing and looks swollen compared to the others. All this leads to questions from new fish owners.

Should you worry about a fat tetra fish? There are several reasons tetra can appear fat. If they are female, they can be pregnant. If they are not pregnant, it can be from feeding, or they have health issues. Either way, you will need to care for your fish more until the large size reduces.

Read on, and you can learn about any health issues there may be, what happens if they are pregnant, and other areas where this swollen appearance can come from.

What if Your Tetra Fish is Bloated?

Although some tetras can be a little fat, you’ll know if your tetra looks bigger than it should. Swelling makes your fish look unnaturally plump. The belly of your fish may look swollen and droopy. This may indicate something simple, like constipation or a serious illness.

Either way, your fish is probably uncomfortable; nonetheless, there are several things you can do to alleviate the symptoms.

Some of the primary reasons this occurs can come from the water conditions in your tank; however, there are other reasons your fish keeps putting on weight.

Bloating may be the side effect of a more intricate problem. Even with treatment, a tetra fish can remain ill. You can help reduce the chance of illness by keeping the tank environment healthy and reducing stress for your fish.


Dropsy is an older term for edema. What this means is there is an accumulation of excess fluids/ water in the body tissues or inside cavities. Dropsy in fish is more of a symptom rather than a disease in its own right. It can be signs of other diseases such as bacterial infections, parasitic infections or liver failure.

Pay close attention to your fish to get a proper diagnosis. Here are visible signs of a fish with dropsy

  • Skin lesions
  • Belling dropping down
  • Scales standing out to the side (looks like a pinecone)
  • Bulging eyes
  • Pale gills

Causes for dropsy come from various areas; however, it is often the Aeromonas bacteria, which causes dropsy.

This bacteria leads to further infection if your tetra’s immune system is compromised. Stress coming from the following can the root cause:

  • Poor nutrition
  • Transportation stress
  • Drops in water temperatures
  • Nitrite and Ammonia spikes
  • Poor water quality
  • Other aggressive fish

Treating Bloated Tetra Fish

Depending on the reason why your fish is bloated, this use of salt can be enough to help treat dropsy and other ailments in your fish. On the other side, many tank experts who see more than one fish suffering the same fate are willing to take the drastic measure of euthanizing all the fish.

If you spot infections early enough, you can segregate them and possibly save them using the following steps:

  • Move your sick fish to a clean hospital tank
  • Add one teaspoon of salt for each gallon of water in your tank. Use aquarium salt or rock salt- never use iodized salt or any that has additives.
  • Feed your fish good-quality foods
  • Treat your fish with prescribed antibiotics in the water or the food
  • Test the water in the hospital tank to be sure it is ideal for your fish

Any fish that show signs of illness do need separating away from other fish. While this can stop any spread of disease, you will need to perform water changes on your main tank as a precautionary measure. From then, you can monitor these to see if they fall to any of the symptoms.

The reason salt baths work is they make the salinity of the water close to that of the fish’s blood. This aids the fish in ridding excess fluids from their bodies.

Pregnant Tetras

Unlike some other aquarium fish, tetras do lay eggs rather than being a live-bearing fish. In many instances, pregnancy is mistaken for illness. Telling a female tetra from a male one can be straightforward; however, knowing if they are about to lay eggs can be another thing.

Males who are growing in the belly department will be sick from the disease.

Many tetras may not display any signs of spawning their eggs, no matter how plump they are looking. In general, a tetra shouldn’t get fat, and it does mean they are ill, pregnant, or there is something wrong with your tank water.

Nitrite levels are one thing that causes tetras to become ill. Be sure your water has levels of nitrites that sit in between 10 and 20 ppm. Frequent water changes can maintain these levels. When you begin looking at their breeding, you can soon learn that a female tetra can breed at 9-months old.

One other thing worthy of noting is tetras can interbreed with other fish. Even though this happens, it isn’t a great scenario because other adult fish can eat the eggs and fry. One other quirk to tetra breeding is the water temperature needs to be certain temperatures. The ideal is 75 degrees fahrenheit if you wish to breed your fish.

If you spot your tetra appears fat in the afternoon to the early evening, this can be they are almost ready to spawn, but as they do this in the morning, they are swimming around with all their eggs still inside.

If your tetra was fat, and suddenly appears back to normal size, check around the gravel as they may have spawned their eggs.

Overfeeding Tetras

If you overfeed any fish, it can make them sick. Tetras are omnivores so that they will eat meat-proteins as well as any vegetable-based foods. In the wild, they are opportunistic feeders; and will eat live plants, algae and many other things. 

The main part of their diet needs to be high-grade foods such as flakes or pellets. They can also have bloodworms, brine shrimp, and daphnia, among others. You can feed these, live, frozen or dried.

When you are feeding your fish, some say twice per day while others say thrice per day. When adding foods, feed for two minutes. Tetras should be able to eat all they require at this time. If they are getting enough when feeding twice per day, you may be overfeeding with the third feeding.

It is common for some aquarium enthusiasts to fast their fish once they see their bellies becoming large. You can do this safely, either for 24 hours or for 48 hours. By the end of this, if they were overfed, you should see a change.

One thing that may prevent a change is your fish are facing some constipation. You can find this condition more often in betta and goldfish, and it stems from a poor diet.

Overfeeding or poor quality food can be the main culprits here. In the cases of poor quality foods, often the fillers cause the issue.

Constipation can be overcome by adding more vegetables to their diet. While doing so, it is worth checking the ingredients on your fish food. Anything with soy or wheat in the first few ingredients are likely to be full of fillers.

To treat tetra that is constipated, the best way is to blanch some peas. Remove the skins and mash the peas with a fork. Because your fish are small, there is enough fiber in the peas to act as a laxative in your fish.

It is advisable to refrain from commercial fish foods and continue with peas, lettuce, cucumber (skins removed), zucchini, and carrots among others. Do this until you see a change, and if there is no change, constipation may not be the issue.

A secondary treatment can be the use of Epsom salts. Once you add these to your tank, they act as a muscle relaxant in the fish, and thus, it should help them have relief from their constipation issues.

The dosage for this is 1 to 3 teaspoons of Epsom salts for every 5-gallons of water.   


There are a few reasons why your tetra can appear bloated. Over the space of a few days, you can see if it is pregnancy in females, or if it is males, then the treatments can help them recover if you spot the systems early enough.

Prompt action can make all the difference between a fish that looks fat to one that is sick and close to dying.

No matter what the symptoms, apart from your fish being pregnant. It shows how important it is to maintain healthy water conditions for all your fish and to feed them a varied diet rather than sticking to one food.