Ich (Ichthyophthiriasis):
This is the most widespread and common freshwater fish disease. The small pustules are actually sacks of tiny protazoans. In a few days, the sacks break open and the parasites fall into the aquarium gravel where they multiply in great numbers. When mature, the new protazoans attack the rest of the fish. It is this lifecycle that makes Ich so contagious. The protazoans will weaken the fish progressively by destroying the protective coating.

The protazoans may only be destroyed after they have left the sacks. When embedded in the aquarium gravel, they are susceptible to medication. Therefore, increasing the temperature of the water during treatment can speed up the life cycle, causing the pustules to break open quicker. After exposed, the protazoans are killed before they can multiply.

Internal Bacterial Infection:
There are many different types of internal bacterial infections. However, they are relatively easy to cure.

Myxobacteriosis:
This infection is rather uncommon but fairly easy to treat. Its probability is intensified by overcrowding and poor water quality with high levels of ammonia and / or nitrites.