Why Is My Neon Tetra Fat And Bloated?

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It is quite common to observe changes in the appearance of aquarium fish. For instance, I have often noticed that my neon tetra becomes fat and bloated. Initially, I was uncertain about the cause of this change, but over time, I have gained some knowledge on the subject.

Neon tetras typically become fat and bloated when carrying eggs, during which they also become very active, develop a bulge in the midsection of their abdomen, and appear relatively wider. However, tetras may also appear fat due to overfeeding, constipation, Dropsy, and tumors.

In the following article, I will explain how to deal with a bloated neon tetra, including testing the water with the API Freshwater Master Test Kit (link to Amazon). I will also teach you how to recognize a pregnant neon tetra and provide a detailed video guide.

Why Is My Neon Tetra So Fat?

Do fish get fat? Well, in the wild, it is rare, if not unheard of. This is because food is not as readily available in their natural habitat.

However, the same cannot be said for fish in aquariums, as they are often overfed. Unfortunately, fish do not refuse food. They will continue eating if you keep feeding them. 

But can you attribute weight gain in every neon tetra to overfeeding? Not necessarily. Like all fish, neon tetras can become fat and bloated for various reasons, including:

1. The Neon Tetra Is Pregnant

Neon tetras are not live-bearers. The females lay eggs that are fertilized by the male tetras. The presence of eggs can cause a female tetra to gain weight.

To determine if your fish’s bloating is a result of breeding, consider the following factors:

  • Gender: Is the bloated fish female? Female neon tetras are larger and fatter than their male counterparts, and they are also less colorful. It is also important to observe the belly area. Female neon tetras typically have a round belly, while males appear flatter, although there may be exceptions to this rule.
  • Behavior: Mating neon tetras tend to chase each other. While this behavior may seem aggressive, it is normal. Neon tetras chase each other when they are about to spawn, during spawning, or after spawning has occurred.
  • Temperature: Neon tetras tend to spawn in temperatures ranging from the low to mid-70s Fahrenheit. Use a thermometer to check the temperature. If the water exceeds that range, the chances of the female tetra being bloated due to carrying eggs are low.
  • Eggs: Search for eggs at the base of the aquarium. On occasion, you may be able to spot them even before the neon tetra deposits them, due to its translucent belly.

2. Your Neon Tetra Was Overfed

This issue needs to be highlighted as it can be dangerous.

Overfeeding is not a mere inconvenience; it can lead to weight gain and pose health hazards such as constipation and swim bladder disease.

Also Read: Neon Tetra Swim Bladder Disease

In many cases, overfeeding needs to persist to cause lasting consequences. It is not advisable to assume that all bloating in neon tetras is a result of overfeeding.

Pay attention to specific signs, including:

  • Duration: Bloating caused by overfeeding does not last long. The bloated neon tetra should regain its original size and shape within a few hours. If the bloating persists, look for additional causes.
  • Behavior: Are your fish constantly hungry? This can indicate overfeeding, especially if you have observed the fish during mealtimes and ensured that they eat all the provided food.

Fish can appear hungry even when they are not, as they may have learned to associate your presence with food. This can happen when an aquarium owner adds food to the tank every time they appear.

  • Food: Examine your tank closely. If you see food on the substrate, you are giving your fish more food than they can consume. Food items like pellets may float on the surface for hours before sinking.
  • Water Quality: Overfeeding can lead to a deterioration in the quality of your tank water. Leftover food in the aquarium can rot and cause spikes in ammonia and nitrite levels. Additionally, neon tetras produce more waste when overfed, which can also lead to ammonia and nitrite spikes.

Also Read: Neon Tetra Swimming Vertically

3. Your Neon Tetra Has Dropsy

Several diseases and infections can cause bloating in neon tetras, but the most significant concern is Dropsy.

This condition causes fluids to accumulate in cavities such as the abdomen, resulting in swelling.

Dropsy is relatively easy to identify. The scales will protrude, resembling a pinecone. 

Additional symptoms include a curved spine, skin lesions, loss of appetite, pale gills, and lethargy, among others.

The condition is often attributed to a bacterium called Aeromonas, though poor water conditions can exacerbate it. Dropsy is dangerous because it affects the internal organs.

4. The Tetra Developed A Tumor

This is one of the worst-case scenarios. Tumors can cause a fish to bloat in ways that give its body an uneven shape.

Some tumors are benign, while others are cancerous. Generally, tumors in fish are rarely treatable unless they can be surgically removed.

What To Do With A Fat Neon Tetra?

Your response to a fat neon tetra depends on the factors that caused the bloating. You need to match the treatment to the underlying cause:

1. Adjusting the Aquarium Conditions

If your neon tetra appears bloated, I highly recommend improving the water conditions. This will benefit the overall well-being of the fish, regardless of the cause of its bloating.

Maintain a temperature of 60 to 75 degrees Fahrenheit, a pH of 6.0-8.0, and a hardness of 2 to 20dGH in the tank. Ensure that the tank has a minimum capacity of 20 gallons.

Adjusting the water parameters will also make it more likely for pregnant neon tetras to spawn successfully. For your convenience, here is the equipment I use in my tank:

Adding plants like Java Fern to the aquarium provides hiding places for the fish.

Don’t forget to monitor the oxygen levels, as oxygen deficiencies can worsen conditions that cause the fish to swell. Install an efficient filtration system to keep the water free from debris.

2. Performing Regular Water Changes

Regular water changes are crucial for maintaining a healthy neon tetra aquarium. An efficient filtration system alone cannot maintain the water’s integrity.

Water changes help combat temperature fluctuations, reduce toxin concentrations, and eliminate bacteria and parasites.

Depending on your water source, you may need to use water conditioners to remove substances like ammonia, chlorine, and copper.

Water conditioners can also stabilize the pH and add essential minerals.

Regular water changes, combined with the use of appropriate water conditioners, will improve the water quality in your aquarium.

This can alleviate stress and promote faster recovery for sick, distressed, and bloated fish.

3. Feeding Your Tetra Properly

Providing a balanced diet consisting of flakes, pellets, cucumber, spinach, and other suitable foods is essential for neon tetras.

Avoid overfeeding by giving them quantities of food they can consume within three minutes. Consider using an automatic feeder for convenience.

Personally, I use the Eheim Automatic Feeding Unit (link to Amazon), which allows me to set the feeding time and ensures equal distribution of food among my fish.

If your fish is constipated due to overfeeding, put it on a diet of peeled and boiled peas for a few days.

You can also treat it with an Epsom salt bath. Once the fish’s constipation clears, the bloated stomach will shrink.

4. Taking Care Of Mating Neon Tetras

Mating tetras should be placed in breeding tanks.

Once they lay their eggs and the male tetras fertilize them, return the parents to the main tank to prevent them from consuming the offspring.

The females should regain their original shape after laying eggs.

5. Dealing With Dropsy

Dropsy often leads to the death of affected fish, which is why many aquarists choose to euthanize fish with this condition.

However, if you are determined to save your neon tetras, you have a few treatment options:

  • Move the affected tetra to a separate tank to provide targeted treatment without affecting other tankmates.
  • Add a teaspoon of salt for every four gallons of water. Salt baths can help remove excess water and reduce swelling.
  • Since bacteria cause Dropsy, the affected fish may respond to antibacterial food. If you don’t have antibacterial food, you can add antibiotics like tetracycline to the tetra’s food.


Here is a brief summary of what I talked about above:

  • Neon tetras can become fat and bloated due to various reasons, including pregnancy, overfeeding, constipation, Dropsy, and tumors.
  • Proper water conditions and regular water changes are essential for the health of neon tetras.
  • Identifying the cause of bloating in neon tetras is crucial for appropriate treatment.
  • Pregnant neon tetras require separate breeding tanks to protect their eggs from being eaten by other fish.
  • Dropsy in neon tetras is a serious condition that often requires prompt and specific treatment.