Is your fish sunburned? He could be if he is exposed to too much light. Unlike humans, who turn red when sunburned, fish begin to lose their coloring when exposed to too much light. The solution is to make sure the aquarium is not in direct sunlight or exposed to ultra violet rays. In addition to sunburn, there are many other skin problems that affect fish, some caused by disease and some caused by environmental factors.


  • Loss of coloration: caused by lighting that is too bright, pH levels too high or too low, medication and diet.
  • Mouth reddish or deep red: caused by mouth fights or cleaning of spawning site (normal and harmless).
  • Body turns black: coloration system is diseased or pinched. (This could also be a malignant growth.)
  • Red dots: louse.
  • Oval objects hanging off the skin: Lernaea.
  • Round, red, inflamed areas: sucking marks caused by leeches.
  • Small, dark, knot-like thickened areas: larvae.
  • Sandy appearance: Ich


Diagnosis can be made by closely observing the skin and other symptoms. Smears and water testing can also help pinpoint the problem so you can begin treatment.


  • Loss of coloration caused by bright light: Provide shady areas in aquarium or move aquarium out of direct light.
  • Mouth fights: Harmless, no treatment necessary.
  • Black body: Consult an aquatic veterinarian. There is usually no treatment.
  • Louse: Treatments for freshwater fish are salt baths, potassium permanganate, Metriforate/Masoten; for marine fish, DTHP and Lindane.
  • Lernaea: For freshwater fish, treat with salt and Metriforate/Masoten; for marine fish, DFD.
  • Leeches: Find the leeches and pick them off with appropriate tools, or remove by applying alcohol topically with a cotton boll.
  • Larvae: No treatment needed.
  • Ich: Currently, a treatment called Fungizone (Amphoterin B) is being tested for treating valuable fishes. If Fungizone is unavailable and you are desperate, try Phenoxethol, an oily liquid, available in stock solution. The solution is added to the aquarium at 40 ml per gallon. Carefully stir it into the water and repeat the treatment again a few days later. You can also use the solution to treat live food, which is a common cause of the disease, but fish will usually not eat food treated with Phenoxethol.


  • Loss of coloration: Good, if caused by too much light.
  • Mouth fights: Excellent, this is a harmless condition.
  • Black body: Fatal, usually a nervous system problem or tumor.
  • Louse: Grave, high mortality rates have been recorded and just one parasite can kill a fish. If the fish do survive the infestation, they often die from a secondary infection, such as septicemia.
  • Lernaea: Good, if the infestation is spotted and treated immediately. These parasites can attach to the heart and skull, which can be fatal, but this is rare. Although they can cause scarring on the fish's skin, they are mostly a nuisance.
  • Leeches: Grave, can cause serious skin damage and death if the infestation is serious. Damage done to the skin can invite secondary infections.
  • Larvae: Good, no treatment needed.
  • Ich: Usually fatal, there is no known cure.


Keep fish out of direct sunlight, keep water clean and make sure the pH is correct at all times.