12 Possible Reasons Why Is My Cardinal Tetra Fat?

Fish living in our aquariums may weigh as they grow older and reach their full size. In addition, some species of fish such as pleco’s and cichlids will often gain weight for reasons we don’t understand since they do not overeat or overfeed themself. But if you have Cardinal tetra and it appears to be fat, they might be a few possible reasons.

Your Cardinal tetra might be fat for various reasons like water quality, stress, and food. Sometimes the mistakes of their owners might also end up making them fat. Along with this, illness and parasites might also be the cause of your fish being fat.

Today, in this post, we will dig in dipper to the possible reasons why your Cardinal tetra is fat.

Can Cardinal Tetra Be Fat?

As we know, Cardinal tetras are omnivores, and in the wild, they feed on small invertebrates, insects, and plant matter. But when you keep them as pet fish, then provide them with good quality food to have a healthy life.

A cardinal tetra can become fat if there is an overfeeding or underfeeding of food, leading to obesity. The condition worsens this species when the fish has poor water conditions. The main reason for having a fat cardinal tetra is that environmental factors lead to stress due to a lack of appropriate environment, temperature, and diet.

Moreover, the love of Cardinal tetras towards plant and animal-based foods leads them to eat more than required.

How To Tell My Cardinal Tetra Is Fat?

Obesity, pregnancy, and bloating are often confusing among fishes. So, some of the symptoms that will indicate your Cardinal tetra is fat are:

A Distended Stomach

Cardinal tetra is a thin-bodied fish with an enlarged stomach when fat. So, if you spot a swollen or bloated-looking midsection on your Cardinal Tetra, then it may indicate that the fish is overweight. However, the abdomen should look relatively flat and never rounded out like an inflated balloon. Also, note whether its scales seem to be sticking out.

A Large Or Bulging Belly

Take a good look at your Cardinal Tetra’s belly to see whether there are any noticeable lumps present under the scales of its stomach area. If you notice an abnormal bulge in this region, it could indicate that the fish has fatty liver disease.

A Dull or Lacking Scales Appearance

Check your Cardinal Tetra for any brownish discoloration on its scales that appears flaking off into the water column. These are symptoms of a condition- exophthalmia. In addition, there is abnormal swelling behind the eyes due to fatty deposits within the head area.

A Loss of Appetite

Cardinal Tetras are very active swimmers, and if the fish is busy swimming throughout your tank all day, then there should be no reason for it to lose its appetite. However, if you notice that your Cardinal tetra has stopped eating or is only picking at food particles, it could mean that the fish is suffering from some illness.

A Dark or Swollen Side

Cardinal Tetras have a light and translucent appearance on their underbelly area with a shiny silver coloration along their flanks. However, if you notice that your Cardinal tetra is getting fat around its sides and has a dark or purple appearance, it could indicate that the fish is suffering from the drop.

A Loss of Balance

Cardinal Tetras are famous for their zippy movements throughout your tank. So, you can always see them darting around with ease. However, suppose you notice that your Cardinal tetra appears to be struggling to swim and is constantly knocking into objects within your tank. In that case, it could indicate that the fish is suffering from some internal disorder.

Head or Tail Biting

Cardinal Tetras are very peaceful fishes, and there should never be any reason for them to start nipping on either their heads or tails with an intense ferocity. Therefore, if you notice that your Cardinal tetra has begun to bite either its head or tail, it could indicate that the fish is suffering from some illness.

Why Is My Cardinal Tetra Fat?

If your Cardinal tetra is overweight, there may be several reasons for this. Some of the causes might be:


If your Cardinal tetra has constipation, it may become obese. The reason is that the fish cannot digest its food properly, which causes an increase in weight gain.

Accumulation of Toxins

If there are toxins in your tank, they might cause obesity in a Cardinal tetra. It will begin to accumulate fat due to this.


If there are tumors in the fish, they might cause obesity as well. The reason is that cancerous cells typically multiply very fast, and this causes a rise in weight gain.

Lack Of Exercise

If you’re not giving your Cardinal tetra enough room to swim and play around in its tank, this could lead to a lack of physical activity. Usually, this, in turn, may cause it to gain weight quickly.


Dropsy is a disease that occurs when the liver of your Cardinal Tetra swells. After which, it can cause scales to appear as if they are ‘peeling.’ It also causes the eyes and stomach to sink in due to this intense swelling.

Fish Tuberculosis

Fish tuberculosis occurs when a bacterial infection affects your Cardinal Tetra over time. The disease damages vital organs, including its swim bladder, leading to issues or collapse.

Viral Infections

Viral infections are the most common causes of illness in Cardinal Tetras. If your fish is suffering from one, its body color will fade, and it’ll have difficulty breathing because of fluid build-up around its heart.

Nutritional Issues

A lack of nutrition can also be why your Cardinal tetra has become overweight or obese. It can be because you’re feeding it the wrong type of food, not giving them enough to eat, or your fish is sick and therefore too weak to search for its food.


If your Cardinal Tetra has become overweight suddenly, this could mean that they are pregnant. It occurs when an egg becomes fertilized inside its body, growing and developing into a baby Cardinal Tetra.

Water Conditions

If you fail to maintain your tank correctly, it can cause water quality to decrease over time, which causes the health of your fish to decline. In addition, it will make them more vulnerable to diseases such as swim bladder issues or Swim bladder disease.


You might be overfeeding your fish without realizing it. It could be due to a lack of time, not knowing how much they should have, or just being too generous with their food portions.


Hexamita is a parasite that infects your Cardinal Tetra and can cause them to become ill. It also causes the fish’s body coloration to fade, an extended belly, along weight loss.

What To Do When You Cardinal Tetra Is Fat?

Once you realize your Cardinal tetra is fat, you should be very attentive to its care. You should provide a larger tank that is more appropriate for its size. You can also divide the fish population between two or three tanks and make sure you change at least 30% of the water every week, using dechlorinated water instead of tap water.

Besides this, you should give more attention to feeding your fish. For example, you can provide your fish with high-quality flake food, sinking pellets, freeze-dried bloodworms, or tubifex worms.

You should also make sure you offer them a varied diet to avoid overfeeding. Finally, do not forget that exercise is essential for all of us, including our fish. A larger tank will allow them to swim around more.

Also, try moving the tank into a different location for six weeks to keep them active and healthy. You can also consider adding some floating plants or creating an aquarium background. It will provide hiding places where your fish could hide when it feels tired of swimming all day long.

What Should You Feed Your Fat Cardinal Tetra?

Cardinal tetras feed on small insects and other tiny organisms in the wild. In a tank environment, you can mimic this by providing your fish with high-quality flake food or freeze-dried bloodworms. It would be best if you also supplemented their diet with vegetables such as cucumber slices to ensure they are getting all of the vitamins and nutrients they need in their diet.

Brine shrimp and algae wafers should only be fed as a treat to your fish because they can cause excess fat gain if provided too often or in large quantities. It is also important not to overfeed them.

How Often Should You Feed Your Cardinal Tetra?

It is essential to feed your fish at least twice a day for them to stay healthy. For example, if you are feeding freeze-dried bloodworms, only give your cardinal tetra as much food as they can eat in two minutes once or twice per day.

When To Feed Your Cardinal Tetra?

It is best to feed your tank fish in the morning and again in the evening. It keeps their metabolism active throughout the day and ensures that they eat at least once per day, if not twice, depending on how much you choose to feed them.

How Much To Feed A Fat Cardinal Tetra?

Limiting your fish’s food intake is essential to prevent excess fat gain. Only feed them as many bloodworms or other small insects as they can eat within two minutes, once every day.

As you can see, maintaining a healthy lifestyle for your cardinal tetra requires commitment on the part of their caretaker. While it may be challenging to adhere to a strict feeding schedule, you should make every effort to do so for your fish to remain healthy and live long lives.

Some Tips For Good Health Of A Fat Cardinal Tetra

Cardinal tetra fish is one of the most popular species in aquariums. But, as with any other type of pet, people often want to know how they can keep their cardinal tetras healthy and happy for as long as possible.

Unfortunately, many new owners don’t realize that this is important to take the responsibility seriously if they want to see their fish live for a long time. So, some tips for managing the weight of fat Cardinal tetra are:

  • Keep the fish in a healthy environment. Clean water is one of many things that can affect an aquarium’s inhabitants’ health. So, if your tank has a problem with cleanliness, it would be better to treat this issue first before moving on Cardinal tetra weight loss plan.
  • Feeding them nutritious food and using vitamin supplements can also help with their weight loss.
  • Keep them physically active as much as possible. If the fish get enough exercise, they will spend more energy and burn calories during playtime than storing them in fat cells.


In conclusion, there are many reasons why your cardinal tetra may be fat. However, the most important thing to remember is that if you think they are overweight, there’s a good chance they are.

It doesn’t matter how much experience you have raising fish or whether or not this is the first time you’ve had cardinals; only an expert can properly diagnose the problem. If you’re not sure, don’t take a chance on your fish’s life!

I hope this post has helped answer the question “why is my cardinal tetra fat?” and that it answers any other questions you may have had as well. Feel free to leave me comments or suggestions below if I missed anything. Thanks for reading!

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