In the present study, the causative agents of proliferative kidney disease (PKD) in both Oreochromis
niloticus and Clarias gariepinus were identified based on the size and morphology of the spores and
their polar capsules. The spores and polar capsules dimensions were measured by the Image J
computer software. The occurrence of different myxosporean spores was confirmed by molecular
biological technique using PCR with general and specific primers for different myxosporeans.
Histopathological changes associated with PKD were recorded in both species. The results showed
that there are 21 myxosporean species belonged to the genera Myxobolus, Chloromyxum, Myxidium,
and Triangula. These include Myxobolus sarigi, Myxobolus amieti, Myxobolus distichodi, Triangula
spp., Myxobolus heterosporous type2, Myxobolus brachysporous, Myxobolus tilapiae, Myxobolus
heterosporous type1, Myxobolus equatorialis, Myxobolus exigus, Myxobolus hydrocuni, Myxobolus
spp., Myxobolus dossoui, Myxobolus heterosporous1, Myxidium spp., Chloromyxum spp.,
Sphaerospora spp., Tetracapsuloid tilapiae, Thelohanellus spp., Henneguya spp., and PKDX tissue
form. The PCR results showed bands at 1600 bp specific for Myxobolus spp., at 450 bp specific for
Chloromyxum (Tetracasuloid spp.), and at 1400 bp specific for Spaherospora spp. in both O.
niloticus and C. gariepinus. The general primer for Myxozoan produced bands at 1700 bp whereas
Myxosprea specific but species unspecific primers produced bands at 900bp. Histopathological
examination showed extrasporogenic stages of the parasite in the kidney interstitium surrounded by
granulomatous inflammatory cell infiltration, while the sporogenic stages were observed intraluminal
or within the epithelial cells of some renal tubules. Necrobiosis of epithelial lining renal tubules was
seen in many affected kidney tissues. Proliferations of interstitial fibrous connective tissue with
degeneration of the renal tubular epithelium were detected in some affected kidneys