Histopathological alterations and condition factor deterioration accompanied by isopod infestation in Tilapia zilli, Mugil capito and Solea aegyptiaca from Lake Qaroun

This study was carried out to identify isopod species implicated in the outbreak that had affected commercially important fishes of Lake Qaroun. The study also aims to determine its deleterious effects on infested fish and its possible role in the severe drop in lake fisheries production. Renocila thresherorum (Crustacea: Isopoda: Cymothoidae) was the only isopod species isolated from the fishes in the lake. The overall prevalence was 38% as 37.14, 25.7 and 53.3% of the examined Tilapia zilli (Gervais, 1848), Mugil capito (Cuvier, 1829) and Solea aegyptiaca (Chabanaud, 1927), respectively, they were found to be infested; while the recorded intensity was 1.23 for T. zilli and 1 for both M. capito and S. aegyptiaca. The main clinical sign noticed was a unilateral or bilateral bulged operculum, with the presence of a large sized isopod female which reached up to 23 mm in length in gill chamber, pale atrophied and eroded gill filament. The condition factor of infested fish significantly decreased in comparison with that of non-infested fish. Various degrees of degenerative pathological lesions including destruction, detachment, hyperplasia and fusion of the primary and secondary gill lamellae were observed in infested fish gills. The current research proved the deleterious effect of R. thresherorum on Lake Qaroun fishes based on clinical finding, condition factor calculation and histopathological examination.