Cymothoids are obligate parasites of marine, brackish and freshwater fishes. They were considered to cause significant economic losses to fisheries through mortalities, stunting growth or damaging tissues of the infested fish. In the last 4 years, lake Qarun suffered from isopod infestation causing fish loss and marketing problems. In the present study out of 375 fish samples belonged to Mugil capito (125), Liza carinata (125) and Tilapia zilli (125) were collected from lake Qarun , El Fayoum governorate and seasonally examined for isopod infestation from the beginning of November 2015 till the end of October 2016. The study revealed the isolation of two species of isopods ; Nerocila orbignyi and Levonica redmani with total infestation rate of 32.53% (21.07% and 11.47% for Nerocila orbignyi and Levonica redmani respectively) with the highest rate recorded during summer. Histopathological study was conducted for estimating the impacts of L. redmani infestation on the affected tissues of M. capito and revealed complete sloughing of the gill lamellae with eosinophilic granular cells infiltration. The study recommended the need to develop a scientific strategy to control the parasitic isopods and prevent its spread among Egyptian water bodies.

Parasitic infestation is considered as serious problem in both wild and cultured fish and has great impacts on the growth, reproduction and survival of their hosts. In Egypt, marine aquaculture is in continuous development so the importance of parasitic infestation studies becomes more evident. The present study investigated the gill parasitic infestation in both wild and cultured Dicentrarcus labrax (Seabass) and Sparus aurata (Seabream ). A total of 236 samples of D. labrax (126 wild and 110 cultured) and 294 of S. aurata (150 wild and 144 cultured) were collected during 2016/2017 from different localities along Mediterranean sea (wild fish samples) and some private marine fish farms (cultured fish samples) in Egypt and examined for parasitic gill infestation. The isolated parasites were identified and the infestation rates of both wild fish species were compared with that of the cultured same species. Results revealed that out of the total examined (530) samples, 378 (71.32%) were found parasitized by monogenean and crustacean parasite species. The examined D. Labrax recorded a total infestation rate of 77.1% where Lernanthropus kroyeri , Caligus species (Copepoda) and Diplectenum aequans (Monogenean) were the most prevalent parasitic species, while Nerocila orbegnyi (isopod) and Furnestinia echeneis (monogenea) were the dominate species among S.aurata which recorded 66.7% as total infestation rate. The study also concluded that gill parasitic infestation rates among the examined wild samples of both fish species were found higher than those of the examined cultured ones. The infested S. labrax gills with Caligus spp. showed excessive mucus secretions and paleness in addition to the detected hyperplasia and necrosis of epithelial cells of primary gill filaments by histopathlogical examination.