الفهرس 
Introduction-
MyxozoaOnly 14 pages are availabe for public view
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Abstract
Many Myxosporidia parasites are widely spread among fish all over the world and it may cause serious changes on fish and affecting the function of their vital organs.
The present investigation was carried out as parasitological survey, histopathological changes and molecular identification of Myxosporidia parasites over one year on 240 fish (120 of Oreochromis niloticus and 120 of Clarias gariepinus) of different sexes and body weights collected from different localities of Assiut city.
Some of the collected Oreochromis niloticus fish demonstrated non-specific clinical signs such as body deformity, skin erosions, fin rot, corneal opacity in one eye, congested gill with excessive mucous and redness of the opercular area. The PM examination of the infected samples revealed darkness of the posterior kidney; pale or congested liver and spleen.
Correspondingly, some of the collected Clarias gariepinus samples demonstrated non-specific clinical signs such as skin erosions, ulcers, blood or black spots, fin rot, pale or congested gills and presence of creamy-white cyst-like nodules on the gill filaments. Moreover, the extra-respiratory organs of the infected fish appeared congested, swollen with accumulation of excessive mucus. In addition, the PM examination of the infected samples revealed discolored kidney, spleen and liver with appearance of whitish small patches on the heavily infected organs.
Results of the parasitological examination of the collected fish revealed that the total infection rate in both fish species was 74.6%, in Oreochromis niloticus, was 65 %, while in Clarias gariepinus was 84.2%.
Four Myxosporidian genera, as single and/or mixed infection, were detected in the examined fish namely: Myxobolus spp, Henneguya spp, Thelohanellus spp and Myxidium spp.
Based on the morphological characterization, twelve species of Myxobolus, two species of Myxidium, two species of Thelohanellus and three species of Henneguya were identified. These different species were detected in kidney, liver, spleen, gills, and muscle of both fish species and Extra-respiratory organ of the catfish. In both fish species, kidney was the highest infected organ with Myxosporidian parasites and the lowest infected organ was the liver.
Regarding the seasonal variation of Myxosporidian infection in the examined fish; the results demonstrated that, the higher incidence rate of infection was observed in winter (76.7%) in Oreochromis niloticus, while summer (93.3%) season had the maximum incidence rate in Clarias gariepinus concerning the examined samples.
Investigation the effect of body weight on the Myxosporidian infection rate revealed the highest prevalence rate occurred in small fish (70-150g) which reached to 75% in Oreochromis niloticus, while in Clarias gariepinus decrease the infection rate with the increase of body weight.
In both examined fish, female’s fish seems to be more sensitive to Myxosporidia than males one.
Several histopathological changes were observed in the kidney, spleen, liver, muscle, gills and ERO of infected Clarias gariepinus and kidney, spleen and gills of infected Oreochromis niloticus.
Based on heavy infection and single infection; four samples (two from Clarias gariepinus and two from Oreochromis niloticus) were selected and subjected to molecular identification of the detected Myxosporidian parasite in these samples. The sequences analysis, BLAST search, and phylogenetic analysis results of the amplified 18S rDNA gene fragment (850bp) from the detected parasites in these samples proved that these 4 parasites represent a new Myxobolus and Henneguya species. The nucleotide sequences of these 4 species were deposited in the GenBank and the following names were proposed for these new species:
Myxobolus asyoclarii (GenBank access number KP990667)
Henneguya asyoclarii (GenBank access number KP990669)
Myxobolus asyotilapii (GenBank access number KP990668)
Myxobolus asyonilotica (GenBank access number KP990670)