Why Do Cardinal Tetras Twitch? | Causes, Exceptions and Cure

Cardinal tetras are beautiful fish that come in various colors and shapes. They live for about five years and can grow four inches long. Usually, Cardinal tetras aren’t tricky to keep in your aquarium, but there are certainly some problems with this fish that you must know beforehand. Twitching in Cardinal tetras and why do they twitch is one of them.

The characteristic of twitching is the erratic movement of the fish. So, there are many reasons why Cardinal tetras twitch. For example, it might be due to an environmental stressor, poor water quality, or disease.

One of the most common causes of twitching in Cardinal tetras is low oxygen levels in the water. Moreover, this can be due to many things such as overcrowding, dirty tank water, or insufficient filtration.

There are many more things that you must know about twitching and why do Cardinal tetras twitch. So, this article serves as a guide to solving the problem of twitching for you.

What Is Twitching Of Cardinal Tetras?

Twitching is a common but serious problem of tetras. It may look like a one-time event. However, it can lead to death if not treated properly. In most cases, twitching happens because of stress or injury caused by other fish in the tank.

Twitching is a process in which the fish’s muscles contract involuntarily. It can lead to muscle spasms and make the fish look like it is “dancing.” But don’t get confused. It is not dancing, but a dreadful disease that needs immediate medical attention to save the fish from dying.

How Does A Twitching Cardinal Tetra Look?

The cardinal tetra is a very slender and well-built fish. When they twitch, it’s easy to see the beautiful coloration of this shy but intelligent species. The pectoral fins are large and spread out in an oval shape at the front of their body while their dorsal fin extends from near their head down their back. The anal fin is located towards the base of its tail.

More often, the twitching Cardinal tetra prefers to rock its body from side to side. This sideways motion usually indicates that the fish is hovering in one spot. While twitching, these fishes will also ignore their food.

At times, the movement of a cardinal tetra appears as swimming in two different directions at once. This odd behavior can last for several seconds or even minutes. In most cases, it’s nothing to worry about, and the fish will return to its usual antics in a short while. However, there are a few instances where the twitching occurs due to an illness or injury and needs treatment.

Why Do Cardinal Tetras Twitch?

There are several reasons why cardinal tetras might twitch. Although it is not unusual for Cardinal tetras to twitch occasionally, when they twitch regularly, there might be something wrong.

Some of the reasons why Cardinal Tetras twitch might be:

Lack Of Oxygen

Usually, when fish are not getting enough oxygen, their sides will start to bulge out. So if you see your Cardinal Tetras doing this, they are trying hard to get more oxygen into their gills.

Cardinal tetras twitch when they are not getting enough oxygen because their gills cannot get the air through the water. To fix this problem, you can increase the water flow in your tank. It will make it easier for them to breathe, and they should stop with their twitching behavior.

Due To Excitment

When a cardinal tetra is excited, it might twitch. While you’re feeding your Cardinal Tetras, they might start to dance around as the food hits the water. This movement is so fast that their tail fin rushes from side to side.

However, you can also interpret the moving of the tail as being attacked – to escape predators – so they will often hide for a short while.


When you keep Cardinal Tetras in overcrowded conditions, they can often become stressed. It might cause them to twitch as a way of communicating their stress to the other fish. When you keep Cardinal tetras with aggressive fish, they might also start to twitch as a way of avoiding aggression.

Algae Growth

An alga build-up on the glass or plants within their aquarium can indicate that something isn’t quite right with water quality. Cardinal Tetras are particularly sensitive to poor water conditions. So if you notice them starting to twitch more than usual, it is a sign that there might be something wrong with the water quality.

Change In Water Chemistry

If the water chemistry changes, it can cause the Cardinal Tetras to twitch. For example, if the pH level of the tank is too high or low, or there is a sudden change in hardness levels, this could trigger a reaction in the fish.


If a cardinal tetra is ill, it might twitch as part of its illness. For example, if a cardinal tetra has contracted an ichthyophagous, it will often twitch as one of the symptoms. The twitching of fish is also common in diseases like dropsy and swim bladder disorders.

Part of Natural Behavior

It is also typical for cardinal tetras to twitch in high-stress situations or if there’s a need to change their environment. However, this isn’t the most likely reason why your Cardinal Tetra has started twitching regularly.

Due To Stress

In an aquarium, without proper cycling, the water quality is poor. It will cause stress in the fish and could lead to twitching. Furthermore, any change in your aquarium water temperature could cause stress and result in twitching.

Sometimes fish will twitch when another fish physically damages them in a fight or if an item is too sharp in your tank. For example, if there are plants with thorns in the tank, the fish sticks on them and start to twitch.

No matter the cause of your Cardinal Tetra’s twitching, it is a good idea to figure out the reason behind this behavior.


There are some exceptions. For example, a fish getting familiar with its new surroundings may twitch on occasion. It is normal, and the twitching will eventually stop over time as the cardinal tetra gets more comfortable with its environment. Cardinal Tetras can also have what seems like seizures during the breeding season if they feel too excited; this is also normal.

Is Twitching Common In Cardinal Tetras?

Twitching is not common in cardinal tetras, but it does occur occasionally. When they do twitch, their fins usually clamp down on one side of the body. It can be a sign that something’s wrong with your water quality or tank environment, so keep an eye out for other symptoms too.

Some of the symptoms that indicate severe twitching is when you find them gasping for air. Their fins clamped down on both sides of the body or twitching paired with other symptoms.

When Should You Be Concerned?

It’s essential to be concerned when you see your fish twitch because it might indicate that they’re severe problems in your water quality and tank environment. If you see any of the following symptoms along with twitching, then it’s time to take corrective action:

  • Gasping for air
  • Fins clamped down on both sides of the body
  • Twitching paired with other symptoms like bulging eyes, red streaks on the body, or labored breathing

How Can You Cure Twitching In Cardinal Tetras?

Notice your cardinal tetra twitching regularly, and it has been doing so for several weeks or months. There could be underlying problems such as illness, injury, stress from overcrowding, or bullying within the tank environment.

So, some of the ways to cure twitching in cardinal tetras include:

  • Adding more plants and decorations to the tank will make it a more comfortable and stress-free environment for them
  • Performing water changes regularly to keep the water quality high
  • Checking the temperature of the water and making sure it is within the recommended range for cardinal tetras.
  • Ensure there is enough oxygen in the water and add an air pump if needed.
  • Introducing new fish gradually to help reduce stress.
  • If all of these measures fail, it may be necessary to move the cardinal tetras to a new tank with more mature fish who will not bully them.
  • If there is no improvement after several weeks, it might be necessary to replace the filter or perform a thorough cleaning of the tank and change all of the water to start afresh with minimal stress for your fish.

How Can You Tell If Your Cardinal Tetra Is Twitching?

There are subtle signs that your fish may be suffering from a twitch. You can usually tell if your cardinal tetra is twitching after it has stopped swimming, for example, when you feed them at the water’s surface, or they are resting on the substrate. When they have finished moving their pectoral fins back and forth in that jerking motion, there will often be tiny little bubbles in the water around them.

So, the signs of twitching in cardinal tetras include:

  • Jerking fins back and forth
  • Tiny little bubbles releases from the fish’s body
  • Fins clamped down on one side of the body
  • Gasping for air

If you’re not sure if your cardinal tetra is twitching or not, it’s always a good idea to watch them for a while and see if they exhibit any of the symptoms mentioned above. If so, then take corrective action right away.


Finally, the most common and likely culprit for cardinal tetras twitch is parasites. You can cure this using a deworming agent specifically made for fish or by adding salt to the water. Make sure to monitor the cardinal tetras after treatment to ensure they are healthy and parasite-free.

There you have it! Now you know all about why cardinal tetras twitch and what you can do to help stop it. Keep this information in mind the next time you are caring for these fish, and be sure to provide them with a healthy, parasite-free environment.

If you have any questions or want more information on cardinal tetra care, please comment below! I’d be happy to help.

Thank you for reading!

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