The white spot disease (also known as ich or ick) is one of the most common parasitic diseases tropical fish aficionados should face in their aquariums.

Being a disease easy to prevent, it is difficult that an aquarist has not seen it in his aquarium.

Was first described in Europe by the aquarium of Hamburg, however the disease is known by the Chinese from very old times, since the Sung dynasty (960–1279 AD).

The white spot disease is caused by a ciliate protozoan (bands of cilia uniformly distributed throughout the body) that it can measure until a millimeter of diameter.

Diagnosis

In the first phase of the illness, when the white spos don't still appear, a change is observed in the behavior of the fish:

• Scratch against stones and decorative objects (the parasite crossed the protective mucous membrane that covers the skin)
• Disordered swimming (even in oblique way)
• The fins folded against the body

Then the white spots of half a millimeter in diameter appear throughout the body. The first spots can be seen in the fins against the light. They are of the size of the head of a pin. As the disease progresses, more spots appear in the rest of the body of the fish.

If the gills are affected, the fish can have difficulties to breathe, reason why they swim in the surface. If the branchial affection is severe, it can lead to death.

When the periorbital tissues and the eye muscles are affected, occurs exophthalmia, ie the protrusion of the eyeball out of the orbit.

The parasite has a well defined biological cycle. It fulfills a free phase, in which it reproduces, and an infecting phase, in which it feeds off of the affected fish.

In the infecting phase the parasite crosses the outer layers of the skin of the fish, it has no preference for any particular tissue, it can affect the skin, the gills, the eyes and the fins.

Produces micro circulatory lesions not detectable with the naked eye, that put in contact the protozoa with the immune system of the fish. The immune system is the responsible for stopping the infection, and attempts to isolate the parasite encasing it with a layer of epithelial cells.

This reaction, known as epithelial hyperplasia, causes the white spots of 0.5 millimeters of diameter, characteristic of the infection.

Since the disease is very contagious, when a fish gets sick the rest of the fish in the aquarium takes very little time in showing the first symptoms.

• Abrupt changes in environmental conditions: For example when replacement water is at a lower temperature than the temperature of the tank water.
• Introduction of fish that were incubating the disease: Fish that carry the parasite and find an aquarium in poor maintenance conditions.
• Introduction of decorations or plants that could carry cysts of the parasite: Boil stones and decorative objects before putting them into the aquarium, clean the plants with a strong disinfectant.

The parasite presents two phases in its biological cycle: a free phase (theront) and an infecting phase (trophont).

In the infecting phase, the parasite attaches to the fish by means of the cilia and begins to penetrate through the outer layers of the skin. In this phase it feeds off of intercellular fluid until reaching the adult state. Increases about 3000 times in volume.

Once the trophont obtained enough reserves, it leaves the fish crossing the epidermis and descends to the bottom producing a capsule called tomont, to start the multiplication by cellular division. The tomont divides itself to produce up to 2,000 ciliated tomites.

The swimming stage of the tomite is called theront. The theront should find a fish in the first 36 hours before its reserves are exhausted and die.

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.

The parasite can only be attacked by medications in the free phase of multiplication in the substrate. In the infecting phase the medications don't reach it, because it is inside the teguments of the fish.

It is convenient to accelerate the biological cycle, by increasing the temperature of the water, for two main reasons:

• To decrease the exposure time of the fish to the parasite (the lesions will be much lighter)
• To increasing the exposure time of the free parasite to the medication (greater number of parasites exposed to the medications and reduction of treatment time)

The temperature of the water can rise up to 30 degrees in tropical aquariums and up to 22 degrees in aquariums of cold water.

The medication for the treatment can be

• Antiparasitic
• Malachite green

If antiparasitics are used, they should be of the antibiotic type selective for anaerobes, this way they don't attack the denitrifying bacteria of the aquarium (which are aerobic).

Malachite green is a dye that effectively combat this disease. The disadvantage is that not all fish tolerate the treatment with malachite green.

The white spot disease is highly preventable disease. The basic measures of prevention are:

• Take care of the conditions of the water in which the fish live, maintaining optimal levels of pH and temperature for the species that inhabit the aquarium.
• Make frequent water changes with quality water, at the same temperature as the water of the community tank.
• Do not buy fish or plants that are in tanks with sick or dead fish.
• Do not introduce fish into the aquarium without observing a quarantine period of at least two weeks.