Help! My Fish Have White Spots!

Oct 24, 2012

White spot disease or Ich (pronounced “ik”) is very common in fish. It can easily spread throughout an entire aquarium.

What does Ich look like?

  • Small white spots can be noted on the skin, fins and gills. Cysts can measure up to 1 mm. In a massive infestation, fish look as if they have been sprinkled with salt or sugar.
  • The signs of the disease are divided into two major categories: cutaneous (the skin is itchy and the fish scratch themselves against the aquarium surfaces) and branchial (more rapid respiration).
  • Secondary bacterial infections are also possible: presence of gelatinous mucus on the skin, or a hole in the skin may be noted.

Some species may have a very severe gill infestation without significant external signs.

What is the cause?

This disease is caused by two protozoa:

  1. Ichthyophthirius multifiliis (fresh water)
  2. Cryptocaryon irritans (salt water)

What is the origin of these parasites?

They can be introduced into the tank through plants and live food. Some fish are carriers or are incubating the disease when they are bought. When they are introduced into the aquarium, they contaminate all the other fish.

Disease Cycle

In order to fully understand how to prevent and treat this disease, it is important to understand its life cycle.

  1. The infectious form (tomite) invades the skin and/or the gills (where it becomes a trophozoite).
  2. The trophozoite encysts in the tissues. The cysts then fall from the fish and settle in the aquarium. Division takes place inside them to form up to one thousand tomites. At maturity, the cyst breaks and releases the tomites into the aquarium.
  3. The tomites must find a host within 24 hours after their "release."
  4. In under-populated aquaria, most tomites do not find a host. In overpopulated aquaria, tomites can accumulate rapidly.

Completion of the cycle depends on the temperature. It takes ten to twelve hours at 26º C, three to four days at 22º C, three to 11 days at 15º C, up to 30 days at 10º C, and probably several months at lower temperatures. The condition can reach epizootic proportions (all the fish are affected). The mortality rate can be very high.


Treatment for this disease is quite simple.

External treatment is ineffective against the forms found in the skin and gills. Treatment therefore focuses on the free-living forms.

a) Ichthyophthirius

  1. First, all fish are placed in a hospital tank for seven days. The main tank is left empty during this period and consequently the tomites die since they cannot find a host.
  2. Second, 80 per cent of the water in the hospital tank is changed twice daily for seven days. This dilutes the parasites and results in their disappearance over time.
  3. Before the fish are reintroduced into the main tank, 80 percent of the water must be changed and the gravel well siphoned.

b) Cryptocaryon

A copper-based treatment is used for Cryptocaryon. For the dosage and further advice, you should consult a veterinarian who specializes in this field.


It is obviously preferable to avoid introducing this disease into your aquarium. All newly acquired plants and fish should be kept in quarantine in a hospital tank for at least 30 days. When the fish purchased are expensive, you can even give each new fish a quarantine treatment in the hospital tank.