Microbtek Lab A local Discus breeder brought a sample of fish to find out the cause/s of fish mortality in his tanks of Discus fingerlings. Every fish that was observed had large number of gill flukes on the gills and Amyloodinium pillularis. Moving gill flukes, Dactylogyrus sp. and club shape Amyloodinium. According to the fish breeder, many Discus breeders loose their fish due to parasitic diseases. Further observation revealed that gastro-intestinal tract of these fish had a large number of internal unicellular parasite, Protoopalina sp. Article By :D.C.Hettiarachchi M.Sc.(Ind.Mcb), PGD (Ind.Mcb), Biol.(B.Sc),br> Industrial Microbiologist Tel. 0769838714; E mail: chris.hettiarachchi@gmail.com