The flagellate protozoan responsible for The Hole in The Head Disease are Hexamita and Spironucleus.
These intestinal flagellates often attack the ornament fish intestines and gall bladder which is fatal if the fish are not treated in time.
The obvious symptom is small holes appear in the body, especially the head region.
The affected fish often stop feeding, develop a hollow-belled appearance, isolate themselves from the others, excrete white and slimy faeces, darken their coloration and exhibit a swollen body.
Hexamita notably affecting fish such as Discus, Angelfish, Oscar Cichlids, Gourami and others.