Your fishes have sings of irritation, weakness, decrease of activity, lost of appetite?. Are they scratching against rocks and gravel? And suddenly they seem to have small white spots on the skin? Yes? Then your fishes probably have a disease calles “White Spot Disease”, “Ich” or “Ick”.
The white spot disease is caused for a ciliated protozoan parasite called Ichthyopthirius multifiliis. In the infecting phase the parasite crosses the outer layer of the skin of the fish. It has no preference for any particular part and it can be in whole body surface, the gills, the eyes and the fins. Usually the first time you see the white spots, they are in the fins. The parasite feeds in the epithelial cells until it is completely mature. The reaction of the immune system fighting against the parasite does the lesions that look like white spots of about
0.5 mm of diameter. When the parasite is mature, leaves the host and encysts in the aquarium substrates and multiplication phase happens. The parasite can only be attacked in this free phase of multiplication in the substrate. The principal treatments are methylene blue and malachite green with or without formaldehyde. Variations in the temperature (high temperature) and water pH (low pH) can help to the elimination of the parasite.