Columnaris, which is a white cottony growth on any part of the fishes' body. 
Hemmorrhagic Septicemia, which has the symptom of red streaks on fins or body of the fish. 
Dropsy or fish bloat, where the scales stand outward and is usually caused by a kidney disorder. 
Costiasis, which is a gray fungus on any part of the body. 
Saprolegnia, which is a true water fungus and causes fin rot. 
Pseudomonas or Aeromonas bacterial diseases, which can lead to mouth rot.