White spot disease (Ichthyophthiriusmultifiliis, or Ich) is one of the most common parasitic diseases affecting tropical fish. It is also, unfortunately, a very persistent disease. White spot is caused when a protozoan attacks and attaches itself to a fish’s body, fins, and gills. The white spots that appear look like grains of salt or sugar, but each one is actually a tiny parasite. They are very damaging to the fish and can cause breathing and mobility problems and even death.

Once the parasites are established in an aquarium, it is difficult to control the infection because they reproduce quickly. If not controlled, there is a 100% mortality rate of the fish in the aquarium. White spot is very contagious. When one fish in a tank gets sick, it won’t be long before the rest of the fish will start showing symptoms. However, with careful treatment of the aquariums fish, water, ornaments, and plants, the disease can be controlled.

Diagnosing White Spot Disease

In the first phase of the illness, before white spots appear, infected fish will display some or all of the following behavioral changes:

  • scratching against stones and decorative objects (the parasite has crossed the protective mucous membrane that covers their skin)
  • disordered swimming
  • fins folded against the body

When white spots appear, they are about the size of the head of a pin. The first spots will appear on the fins and can be seen in direct light. As the disease progresses, more spots appear on the rest of the fish’s body. If the gills are affected, the fish may swim to the surface more than usual. This is because they are having difficulty breathing. When the peri-orbital tissues and the eye muscles are affected, the eyeball will protrude.

Treatment for White Spot Disease

Medications:The Ich parasite can only be attacked by medications at a very specific point in their life cycle. Medication can work during what is called the “free phase,” when the parasite is multiplying. Once the infection phase has begun, medication will not work because the parasites are inside the fish’s tissue.

Effective medications include:

  • anti-parasitic medicines
  • malachite green

Anti-parasitics should be of the antibiotic type, specifically for anaerobes. This way they don’t attack the aerobic de-nitrifying bacteria in the aquarium.

Malachite green is a dye known to effectively combat white spot. A disadvantage to this method is that not all fish can tolerate the treatment.

Higher Temperature:

It is possible to combat the parasites by accelerating their biological cycle, thereby decreasing the window of exposure opportunity and making medicines more effective. One way to do this is to increase the water temperature.

Raising the temperature of tropical aquarium water to 30 degrees Celsius (86 degrees Fahrenheit) and cold water aquarium to 22 degrees Celsius (71.6 degrees Fahrenheit) can be very effective in the early stages of the illness.

What Causes White Spots?

This disease can be caused by:

  • Abrupt changes in environmental conditions, for example if replacement water is at a lower temperature than the temperature of the tank water.
  • Introduction of fish that were incubating the disease into a poorly-maintained aquarium.
  • Introduction of decorations or plants that are carrying cysts of the parasite.

Preventing White Spots

White spot disease is easily preventable. Some basic measures to maintain a healthy, parasite-free aquarium include:

  • maintaining optimal levels of pH and temperature for the species that inhabit the aquarium
  • frequent water changes with high-quality water that is the same temperature as the water of the community tank
  • purchasing fish and plants that come from healthy tanks
  • observing a quarantine period of at least two weeks before introducing new fish
  • boiling stones and decorative objects before putting them into the aquarium
  • cleaning new plants with a strong disinfectant

How White Spot Parasites Work

The parasite that causes white spot disease has a unique biological cycle. In its free phase, it reproduces. In its infecting phase, it feeds off of the tissues of affected fish. In the infecting phase, the parasite crosses the outer layers of the fish’s skin. It has no preference for any particular tissue. It can invade the skin, gills, eyes, or fins. Once attached to the fish’s body, the parasites produce micro-circulatory lesions that cannot be seen with the naked eye. These put the protozoa in contact with the fish’s immune system. When the immune system reacts to stop the infection, it attempts to isolate the parasites by encasing them with a layer of epithelial cells. This reaction is known as epithelial hyperplasia and it causes the white spots.

Once the parasite is big enough, it leaves the fish and descends to the bottom of the tank. Then it multiplies, producing up to 2,000 new parasites. The duration of the biological cycle varies with the temperature of the water:

  • At 25 degrees: 3 to 6 days.
  • At 15 degrees: 10 days.
  • At 10 degrees: 25 to 30 days.