A total of 556 fish represented by 180 Solea Solea, 203 Tilapia zilli and 174 Mugil capito were collected from Qaroun llake, Fayoum province, Egypt. They were investigated for Isopods infestation during the period from June 2015 to September 2016. The total prevalence was 33.5% ,41.1% and 80.9% in T. zilli, Solea solea and Mugil Capito; respectively. Four cymothoid isopod species were encountered among the examined fish: Anilocra physodes was perceived from Solea Solea, Nerocila orbignyi from Mugil capito, Solea solea and Tilapia zilli. Renocila thresherorum from Tilapia zilli. Lironeca ovalis from both Solea solea and Mugil capito. All the recovered Isopoda showed seasonal variations in the rate of infestation, reaching the peak in summer. The histopathological alterations induced by isopod species were discussed. Furthermore, the efficacy of some herbal extracts as neem leaves extract (Azadirachta indica), chamomile flowers extract (Matricaria chamomilla) and shih (Artemisia herba-alba) was evaluated in vitro against isopod parasites and they were compared with deltamethrin bath as a chemical drug.