Fish health and welfare

Signs of a healthy fish

  • Appetite: Good, food eaten swiftly and enthusiastically.
  • Breathing: Gills should rise and fall rhythmically. Fish continuously gulping at the surface (except labyrinth species, e.g. gouramis) is a sign of oxygen starvation or poor water quality.
  • Demeanour: Active, alert and sociable. Lower activity levels could indicate a temperature drop and a fish that leaves the rest of its shoal may be sick.
  • Eyes: Bright and clear.
  • Fins: Intact, watch out for tears, splits, spots or streaks of blood. Fins should also be held away from the body, not drooping or folded.
  • Position: Freely and evenly swimming, a fish either sinking to the bottom or swimming to one their side is a bad sign (some catfish do swim upside-down normally, though!).
  • Scales: Should show no injury or fungal growth.
  • Vent: Clean and without stringy faeces.

Signs of poor health

  • Sunken or distended bellies (except when carrying eggs).
  • Sticking out scales.
  • Pale patches on scale.
  • Tiny white spot.
  • Milky eye.
  • Irregular position.

Common ailments

  • Oxygen starvation: Gasping at the water surface.
  • Fungus disease (saprolegnia): Body and fins covered in white tufts (if around the mouth then 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 etc which will heal on their own).
  • Dropsy: Bloated body and protruding scales.
  • Swim bladder disease: Loss of balance leading to 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.


Most of these conditions are caused by poor water quality and so if you notice any of these issues, you'll need to check your water quality first. Download our freshwater fish care sheet (PDF 556KB) for information on maintaining good water quality.

See the Tetra website for help identifying some of these fish parasites and the medications that can be used. Also read more about fish diseases on the Practical Fishkeeping website.

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

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