The proliferative kidney disease (PKD) has been documented to cause particular economic loss in fish
farms worldwide. The present investigation aims to determine the prevalence and the etiology of
(PKD) in Oreochromis niloticus and Clarias gariepinus obtained from El-Riah El-Tawfiki and its
tributaries. To achieve this goal, 500 fishes were used of which 266 were O. niloticus and 234 were C.
gariepinus. The fishes were dissected and the kidneys were examined macroscopically for the
presence of morphological abnormalities and nodules. Fresh and Giemsa-stained slides of kidney
tissue were also examined for determination of the causative agent. The results showed the prevalence
of PKD in O. niloticus was higher in autumn (95.08%) and spring (91.94%) than in summer (76 %)
and winter (73.53%). The prevalence of PKD in C. gariepinus was high in winter season (76%) and
low in spring season (36.84 %). The overall prevalence of PKD was higher in O. niloticus (83.46%)
than in C. gariepinus (46.58%). The Clinical signs of fish affected with PKD may be non-specific
included distended abdomen with dark color, anaemia with pale gills and emaciation. Some fish have
nodules in the eye around the iris forming a ring. Macroscopically, there was enlargement of the
kidney with appearance of some kidney nodules of approximately 0.2 – 0.6 mm diameter. Based on
the spore morphology, the causative agent was identified as different types of Myxosprean spores in
O. niloticus and C. gariepinus. The high prevalence of PKD in both types of fishes suggests the need
to establish strict control measure to overcome the great economic losses imposed by the disease