You asked in a thread what the causes of hole-in-the-head disease were? It's hexamita, a parasitic disease. It primarily affects only cichlids, though. When the little parasites invade the body, they can sometimes be carried through the bloodstream to the sensory pores in the head. This is what causes the holes. It doesn't always happen with hexamita but when it does, it becomes hole-in-the-head disease.