Aquatics Unlimited: Articles: Sick - or Infected?
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Sick - or Infected?

for the week of 12/10/98

Many aquarists assume sickness and infection are all interchangeable terms and go on to treat every fish that has torn fins, cloudy eyes, or abnormal swimming behavior with antibiotics or other medicine. This course of action is often unsuccessful or even counter-productive.

"Sickness" is a rather broad term, simply used to state that something is affecting the fish's well-being. This could be a parasite, bacteria, or other infective agent, but it could also be a water quality or temperature problem, organ failure, or even the aggression of a tankmate. For example, a "sick" goldfish might be swimming at the top of the tank because...

  • it has gill flukes
  • it's gills have been damaged
  • there are high ammonia or nitrite levels in the water
  • there is little dissolved oxygen in the water
  • the temperature is too high
  • another fish chases it whenever it comes down

Adding medication might be of value in some of these situations, but would be useless or could even worsen the others.

Infection is a much more precise term, referring to sickness that is caused by parasites, bacteria or some other organism that has taken up residence in or on the fish. Of the above six examples, only the first (gill flukes) is an example of an infection. Other examples are:

  • White Spot Disease (Ich)
  • Bacterial Fin Rot (Columnaris)
  • White Cotton Disease (True Fungus)
  • Viral Cauliflower Disease (Lymphocystus)

Medication would very likely help a fish with any of the first three infections (viral infections are virtually untreatable), but even then, care must be taken that the medication match the type of disease involved. All four of the above might be commonly described as "white spots" on the fish, even though they are caused by parasites, bacteria, fungus and virus respectively.


"Tip of the week" appeared regularly in 1999 and 2000.

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