Abstract
Originally, Myxobolus fahmii was described from the gills of Barbus bynni collected from the Nile River, Egypt. The original study provided only mensural characteristics of the spores and referred to gill lamellae as the site for the infection. In this study, B. bynni were collected from almost the same locality, with a similar parasite being found. Our investigations enabled us to determine the precise infection site, which corresponded with the "filamental vascular type" and to provide, for the first time, information on pathogenicity and on the seasonal variation in the prevalence of M. fahmii in gills. The infection was recorded as whitish ellipsoidal plasmodia within the afferent artery of the gill filaments. Due to continuous growth of the plasmodia, gill lamellae were atrophied and obliterated at the plasmodium site. Spores were drop to ovoid shaped with a mean length of 11 mu m and mean width of 8 mu m. Polar capsules were pear shaped, measuring 7 mu m in length x 3.0 mu m, with 5-7 filament coils. The overall prevalence of infection was 32.9 % (79/240). The highest prevalence was in autumn 63.3 % (38/60) while the lowest was in winter 6.6 % (4/60). The infection showed a significant difference in prevalence between all the seasons except autumn and spring and summer and winter.