Endoparasites are parasites which live inside the fish. Ectoparasites are parasites which live on the outer surface of the fish's body such as skin, gills, etc.
Endoparasites are relatively rare among aquarium fish. These include worms which live in the intestines. Endoparasites can be treated with water based medication or with medicated foods.
Ectoparasites include leeches, Fish lice and Anchorworms. Ectoparasites can be identified easily. Ectoparasites are usually treated with water based medication.