Prevalence of parasitic isopods (Cymothoidae and Gnathiidae) on Actinopterygii fishes from the Alexandria coast off the Mediterranean Sea, Egypt

During the year 2021, a total of 2152 Actinopterygii fish represented by eleven fish species were collected from the Egyptian waters of Alexandria. Livoneca redmanii Leach 1818, Anilocra alloceraea Koelbel 1878, Ceratothoa oestroides Rosso, 1827) (family: Cymothoidae), and Gnathia sp. (praniza larvae) (family: Gnathiidae) were discovered throughout the research period. The current study aims to provide insight on the distribution of parasitic isopods among infested fish on the Egyptian coast, through associations between parasitic species and their hosts. Two of the four species (C. oestroides and A. alloceraea) were reported for the first time on the Egyptian coast. Among the six host species, Gnathia sp. (praniza larva) has consistently been proven to be the most frequent species. Gills of four host species have been implicated in the discovery of Livoneca redmanii. The buccal cavity of Boops boops (Linnaeus, 1758) has been gathered to have Ceratothoa oestroides. whereas Anilocra alloceraea were reported on the outer body of Sardina pilchardus (Walbaum, 1792). L. redmanii and Gnathia sp. which parasitized of Scomberomorus commerson (Lacepède, 1800) and Pomatomus saltatrix (Linnaeus, 1766) had the greatest prevalence rates across their host species (P=27.1% & P=17.7%), respectively. The bulk of the host species infection sites is found on the gill macroniche of the hosts, which account for 580 parasitic specimens out of a total of 978 for Gnathia sp. L. redmanii followed with 162 parasitic individuals out of a total of 174 individuals. Our investigation concluded that the parasites select a particular host to access it secretly, in a situation known as the host's specificity. New hosts that included L. redmanii on P. saltatrix, S. commerson, and Umbrina cirrosa (Linnaeus, 1758) have been reported.