Three hundred and fifty naturally infested Oreochromis niloticus fingerlings were collected from a cultured fish farm. They were examined for external Protozoa, monogenetic and digenetic parasites. The prevalence of isolated
Protozoa showed high infestation rates with Trichodina mutabilis (71.3%),Chilodonella hexasticha (60%). Monogenetic flukes (Gyrodactylus rysavyi) had infestation rate of 40%, while digenetic larvae (Hetrophyid metacercariae)
showed an infestation rate of 66.6%. The morphometric characters of isolated parasites were determined. Anorexia was the main clinical sign recorded with  slimness of the skin, presence of scattered haemorrhagic spots, detached scales
and restlessness. Mortality rate was 15 % among examined fish. Comparative treatment of the infested fish with formalin (20 ppm) and potassium permanganate 2 ppm for 48 hr bath was recorded. Besides, the
adverse effects of such drugs on water quality were studied. Such drugs showed effectiveness against Trichodina, Chilodonella and Gyrodactylus, although marked decrease in dissolved oxygen and increase in nitrite was recorded. The
value pH decreased in case of formalin and increased in case of potassium permanganate.