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What Does A Sick Fish Look Like?

Updated on October 14, 2009
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Oftentimes we are told to watch out for our fishes health, but many times we don't know until they start 'swimming' belly up that there was anything wrong with them at all. This is particularly common amongst children's pet fish as they may not be as well cared for as more expensive aquarium fish.

Here are a few signs that your fish is sick.

Sick Fish Symptoms

Behavioral Signs

  • Listless, does not have much energy.
  • Difficulty swimming, tending to swim on one side or the other.
  • Swimming nose down or tail down.
  • Fins clamped together.
  • Scales puffed out like a pine cone.
  • Breathing hard when doing little to no swimming
  • Swimming near the surface and gulping for air.

Physical Signs

  • White spots.
  • Red spots.
  • Sores or lesions on the skin.
  • Frayed fins
  • White fins
  • Inflamed fins.

If your fish displays any of these symptoms, they need your help now. Click here to read about specific diseases and cures, but first, perform some basic first aid.


Test The Water

The very first thing you need to do when you notice a sick fish is to test the water. Test for ammonia, nitrites and nitrates. If any of these are too high, do a 50% water change. Poor water quality is the leading cause of fish deaths. If you don't own a testing kit, buy one. There is absolutely no other way of telling if the water quality in your tank is poisonous or not. You can have crystal clear water and dangerously high ammonia, nitrite and nitrate levels.

Most fish diseases can be prevented or at least minimized by having very clean water and healthy conditions. You may inadvertently be overfeeding your fish, which could lead to water quality problems and an environment in which bacteria can flourish. If you experience many problems with sick fish, try doing water changes more often and make sure your tank is cycled.

Add Oxygen

If your fish are gulping at the surface of the tank, there is not enough oxygen in the water. Low oxygen can be a cause of stress to your fish and many fish medications will remove oxygen from the water, making it all the more important for you to increase the levels of available oxygen. Adding an air stone attached to a pump is an excellent start.


If your fish is in a tank full of other fish, quarantine it before it has a chance to spread the disease to the others. All new fish should spend a minimum of a week in a quarantine tank before they are released into the main tank.

Remove Carbon Filters

Carbon can soak up medication, rendering it useless. If you use carbon filters, take them out whilst you are medicating your tank.

Need more help? Read more about fish diseases and how to treat them....


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      angela 6 years ago

      my fish just mated 3 days ago and he looks like he has fin rotting or he is sick what should he do p.s he is a betta fish

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      crystal 8 years ago

      my batta fish is acting funny. I bought him yesterday at petco (where the pets go)

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      Tamarind 8 years ago

      Very straight forward hub. All the info is there. I think this hub is a good quick reference for when your fish looks sick.