TIP from FNM: Fish Behaviour - Pain & Stress

Behaviour relevant to pain and stress:

  • Feeding activity can be a basic reaction to pain.
  • The initial reaction of the fish is often a sudden drop in feed consumption, resulting in cessation of feeding.


  • Estimation of swimming ability can provide sensitive index to general stress and pain in fish.
  • The swimming ability of fish under painful conditions, compared with that of a healthy fish, is different.
  • The pattern of swimming: swimming into shallow water, swimming lethargically at the surface, lying listlessly on the pond or tank bottom, floating downstream or swimming erratically can be an indicator.


  • It is also thought to be a useful means to gauge the pain in fish.
  • A difference between resting and active metabolism can be quantified simply by counting breaths (opercular beats) per minute or more precisely, by measuring respiratory gases.
  • Respiratory movements, and even oxygen consumption all provides measures of toxicological stress which is related to pain by the fish.

Clamped fins:

  • The fish clamps its fins close against its body. Experienced aquarist use this to quickly spot problems with their fish.


Looks like the fish is swimming fast but staying in the same place. 

  • Fins will be continuously beating but fish almost stationary (not moving)

Ich spots:

  • Ice looks like tiny white spots on the body and fins of the fish. This is a common disease 
  • Fish may show "flashing behaviour" or rubbing its body against any surface
  • When disease progresses, it would become lethargic and settle at the bottom of the tank

Red or white sores:

  • Many things can cause sores on fish such as fights with other fish, scraping on sharp rocks, and small wounds that get infected and grow bigger.

Gasping at the surface:

  • A fish that is gasping at the surface of the water is usually:
- suffering from a lack of oxygen, that could be due to a lack of oxygen in the water or
- the fish's inability to absorb the oxygen from the water
  • Check the aeration, or partial water exchange
         If only one or two fish gasping, but the other fish are normal, then water probably has plenty of oxygen and should immediately treat the gasping fish.
If there is possibly lack of dissolved oxygen in the water, immediately do all of the following:
  • Check the filter; ensure that it is working properly. If it is not working properly, immediately fix it. 
  • Check the temperature; of water on the thermometer, if aquarium has a heater. If it is not in the range, adjust the temperature using chiller or heater.
  • Check the water surface; if there is oil or scum then carefully scoop water off the surface until you've removed two inches of water. Replace this with fresh water. You can also add aquarium salt or water conditioner to it.

Crashed on the bottom:

  • When fish crash onto the bottom of the tank and do not swim, it is usually a sign that they are exhausted.
  • There are many reasons a fish can become exhausted, but quite often, they are sick and have probably showed symptoms such as gasping, shimmy or clamped fins, before they become tired and crash on the bottom.


  • Behaviour where a fish rubs itself on the bottom of the fish aquarium, or on the gravel, or on a rock or ornament. The fish rubs or glances because it is itchy.
  • An itchy fish often develops more serious signs of stress and disease. If you see your fish glancing, you should immediately treat your aquarium.
  • There is a chance of parasitic infections.

Loss of appetite:

  • If your fish is not eating or takes food into its mouth and then immediately spits its out, your fish is showing one of the Signs of Stress and Disease.
  • You should make sure that other fishes in the tank are not making this fish feel miserable, for example, bullying.

Other signs of stress:

There are many other signs of stress and disease in fish such as

  • "fin rot" where the edges of the fish's fins disintegrate, or 
  • "pop eye" where the fish's eye bulges out, or 
  • "cotton mouth" where the fish has patches that look like cotton around its mouth,

But most of these are more pronounced signs of stress and disease occur after the more subtle signs of stress and disease that are discussed before. Sometimes "fin rot", "pop eye", "dropsy", and "cotton mouth" are difficult to cure. But before they occur, the fish often shows milder signs of stress and disease such as clamped fins. If you treat a fish at the sign of stress and disease, you'll have a much better chance of curing it.

Take Immediate Action

If you have seen any of the symptoms listed above or if several fish have recently died in your aquarium, you should immediately take action and treat your fish. 

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