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Why Are Your Tropical Fish Twitching? 4 Reasons 

5 min read

With their vibrant colors, tropical fish can be relaxing to watch as they swim about their day in your aquarium. But once in a while, they may act strange. For example, why is your tropical fish twitching?

Tropical Fish

Your tropical fish may be twitching due to extreme stress. Something may be wrong with the water, the fish may be bullied by a tank mate, or the fish may be ill. On occasion, the fish may just be itchy.

It is important to figure out whether these fish convulsions are something minor or something serious.

This article will cover why your fish is shaking and how to stop the twitching to return your fish to their healthy selves.

Let’s get started.

Why Are Your Tropical Fish Twitching?

Your Fish Feels Itchy

Fish twitching may simply be a sign that your fish is feeling itchy – as with humans, a little itch here and there is probably nothing to worry about. Since they have no hands, they resort to twitching.

A seemingly random twitch or rubbing against something in the tank may be your fish’s version of a good scratch.

If you see your fish twitching at the bottom of the tank, it is probably trying to scratch itself against the gravel. It may also use other objects in the aquarium such as rocks or wood.

For more info, including how to tell if a fish is simply itchy or if it’s something to be worried about, read this article.

However, if the twitching is constant or severe, there could be some other underlying cause.

Tropical Fish

Something in the Water Is Wrong or Out of Balance

Stress is the main reason for a fish to be constantly twitching. This involuntary behavior can manifest in just one part (e.g., the fins) or the entire body. If your fish is rocking back and forth, that’s a type of twitch known as ‘shimmying.’

The fish shimmying may be due to environmental factors, such as:

  • Poor water quality
  • Uncomfortable temperatures
  • Hunger
  • Boredom
  • Poor water circulation

Toxic chemicals such as chlorine and ammonia can cause skin irritation, leading to shimmying fish.

Also, if the water pH is too high or too low for your fish, it may cause them to act erratically.

Tropical fish require warm water; if it is too cold they could become stressed. Prolonged low temperatures could make them sluggish and lower their immune system.

The Fish May Not Be Getting Along With the Others

It’s possible that one or more of your fish are getting bullied by their tank mates. Just like people, bullied fish become stressed, which can manifest as twitching. You may have inadvertently mixed two different species (or two different personalities) that just clash with each other. 

Furthermore, some fish twitch at each other when they become confrontational; an example is the angelfish.

So if you see two of your fish twitching at each other, there’s absolutely nothing wrong with them – other than their behavior.  

If your fish are the freshwater variety, here’s an article on freshwater fish that can live together.

The Fish Is Sick

Finally, a tropical fish may twitch because of illness. The fish spasms are a symptom rather than a disease of its own. Signs of a sick fish include:

  • Irritated/swollen gills or eyes
  • Missing scales
  • Damaged-looking fins
  • Dull color
  • Not eating
  • Lethargic behavior

If your fish is twitching or shimmying constantly, it means something is wrong with its nervous system. The convulsions occur when they lose control of their nervous system.

Certain tropical fish species are highly susceptible to this condition, including mollies, guppies, swordtails, and platies.

Sometimes, twitching will be due to an ectoparasite that burrows onto the fish’s skin. Ich is an example – look out for white spots on the skin. 

How To Keep Your Tropical Fish From Twitching

Keep the Water Temperature and Chemistry at Optimal Levels

When your fish seems stressed, the first thing you should do is check its tank and ensure that the environment is suitable for your pet.

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For tropical fish, the water should be between 76-80°F (24.5-26.7°C). You can install a heater for your tank, such as this Orlushy Submersible Aquarium Heater (available on The heater is available in multiple power levels for different tank sizes and has a thermometer to help you gauge the water’s temperature. 

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Likewise, pH levels and the overall water chemistry (nitrate, oxygen, and ammonia levels) must be checked regularly. There are multiple test kits you can use to check for pH, water softness, and other vital statistics. One option on Amazon is these PULACO Aquarium Fish Tank Test Strips (available on Each strip tests the levels of pH, nitrate, nitrite, chlorine, carbonate, and water hardness. 

This YouTube video covers the basics of pH, GH, and KH levels in an easy-to-understand format:

Clean the Tank Once in a While

A clean tank is a healthy tank: you can eliminate a lot of the issues by cleaning out your tank and changing the water.

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If you can barely see anything in the tank due to all the algae, it’s probably time to clean it up. You can also install something like the Aqueon Aquarium Algae Cleaning Magnets (available on It allows you to clean the tank from the outside, and it comes with a 90-day warranty.

Be careful when changing the water though, as your fish wouldn’t like the abrupt change to its environment and would likely become stressed. Many hobbyists have observed their fish starting to twitch immediately after a water change.

In case you want to know how much water you need to change, I’ll point you to another article.

Nip the Bullying in the Bud

Watch how your fish behave towards each other, especially at feeding time. If a fish is frequently nipped at or chased, that can lead to high stress levels and twitching.

Get a larger tank so that your fish have ample space to leave each other alone. Get aquarium plants, rocks, and driftwood to create spots where your fish can hide.

As a last resort, you may have to separate fish that are too aggressive from the others

Get Help From a Veterinarian

If there’s a veterinarian in your area, it may be a good idea to give them a call ASAP. Ideally, your vet should be experienced in treating tropical fish.

Final Thoughts

I hope the above information helps you figure out why your fish is twitching and how you can put an end to it.

You cannot just sit back and enjoy the view your aquarium provides when your fish is convulsing.

Sometimes, it is nothing serious and will pass, but you still need to eliminate some of the worst-case scenarios.

A good aquarium keeper is a keen observer of the fish they keep so that they are always aware of what their fish are going through. So keep your eyes peeled.

Thanks for reading.

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