The increased production of mucus in aquarium fish will be visible as cloudy patches on the skin, particularly along the flanks. Because of increased mucus production around the gills, affected aquarium fish often show signs of respiratory distress such as heavy or labored breathing. Irritation of the skin causes aquarium fish to scratch themselves against solid objects. Lethargy and loss of appetite are also common as the aquarium fish becomes increasingly stressed. In extreme cases obvious physical damage to the skin occurs, and secondary infections such as fungus and finrot can develop.
Fish & Aquarium Supplies: Bacteria & Fungus Medications
Almost all types of fungal disease -- and bacterial diseases that get lumped in with them -- are opportunistic infections. This means the organisms that cause these illnesses live in most aquarium water and even in fishes' bodies. These organisms cause disease only when something else goes wrong. When a betta is kept in unhealthy conditions, it is more prone to developing opportunistic fungal infections. You can limit risk of such infection by keeping a betta in a real aquarium with light current.
How to Treat Fungus on Aquarium Fish | eHow
Bettas, also called Siamese fighting fish, can tolerate less-than-ideal aquarium conditions, but to thrive, they need certain water quality and plenty of space. Though bettas can survive in a small, room-temperature bowl, they're going to fare better in a real, heated aquarium. In cramped, unhealthy conditions, bettas succumb to various diseases, including several types of fungus.
How to Treat Fungus on Aquarium Fish