Additional morphometric and phylogenetic studies on (Isopoda: Cymothoidae) parasitizing the Red Sea fish in Egypt.

Cymothoidae, Leach, 1818 (Crustacea: Isopoda) are ectoparasites of marine, brackish and freshwater fishes that are reported to induce deleterious tissue impacts on the infested fish hosts. The present study aimed for the first-time screening of collected from the red sea fish in Egypt. Surveillance study was conducted for isopod infestation among the Red Sea fish revealing a total infestation rate of 40.96% with the species identified as . The parasite species was isolated from the branchial cavity and gills. Morphometric description was estimated using dissecting stereo-microscope, and scanning electron microscope (SEM) provided new additional features for the isolated species including the microtrich sensillum in the body cuticle and the fine structure of the mouth parts and body appendages. Mitochondrial gene of female isolated in the present study from was detected for the first time in Egypt and recorded in the GenBank (MK168807). The study showed that the detected isopod species represents one monophyletic group closely affiliated to the genospecies of , and can be distinguished clearly from other isopods genospecies. Based on the genetic distance values, lower level of genetic divergence was indicated within the genospecies of the present isolated from Egypt and the same species isolated from India. The present investigation recorded fish as a new host for the isopod in Egypt and provided additional morphological features through SEM as well as molecular characterization of this isopod species for the first time.