Fish health and welfare

Find out how whether your fish are healthy or unwell with these handy checklists. 

Signs of healthy fish

  • Good appetite: Eating quickly and enthusiastically     
  • Breathing well: Gills rising and falling rhythmically
  • Behaviour of fish: Active, alert and sociable
  • Eyes are bright and clear
  • Healthy fins: No sign of tears, splits, spots or streaks of blood. Fins should also be held away from the body, not drooping or folded    
  • Swimming freely and evenly
  • Healthy scales: No sign of injury or fungal growth      
  • Clean vent without stringy faeces

Signs of poorly fish

  • Sunken or distended bellies (except when carrying eggs)
  • Sticking out scales
  • Pale patches on scales
  • Tiny white spots on the fins, gills or skin
  • Milky eye
  • Swimming unusually: A fish either sinking to the bottom or swimming to one side is a bad sign. Some catfish do swim upside-down normally, though!    
  • A change in activity levels: Could indicate a temperature drop. A fish that leaves the rest of its shoal may be sick
  • Oxygen starvation: If a fish is continuously gulping and gasping at the surface (except labyrinth species, e.g. gouramis) is a sign of oxygen starvation or poor water quality
  • Fungus disease (Saprolegnia): Body and fins covered in white tufts. If they're around the mouth, then it's likely a different condition known as 'Mouth fungus'
  • White spot disease (Ichthyophthiriasis): Tiny white spots covering skin, gills and fins
  • Fin rot: Wasting of the tissue between fins - not to be confused with accidental tears, which will heal on their own
  • Dropsy: Bloated body and protruding scales
  • Swim bladder disease: Loss of balance leading to the inability to swim properly      
  • Temperature stress: If the water becomes too cold, tropical fish are known to swim slowly. If too hot, the oxygen levels will decrease, so the fish will gasp at the surface.

Treating a sick fish

Most of these conditions are caused by poor water quality. If you notice any of these issues, check your water quality first. 

Download our freshwater fish care sheet for information on maintaining good water quality.

Visit Tetra for help identifying some of these fish parasites and the medications you can use, and read more about fish diseases at Practical Fishkeeping.

If you need help in diagnosing and treating fish disease, please contact a specialist fish vet.

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