In the present investigation, we identified a cymothoid isopod species, Livoneca redmanii (Isopoda, Cymothoidae), in the branchial cavity, skin, and muscle pouch of the common sole (Solea solea) (Soleidae, Pleuronectiformes) from Qarun Lake, Egypt. The parasite was identified by morphometric and ultrastructural analysis, and molecular typing of the 16S rRNA gene. Out of 625 S. solea specimens collected, 8.16% were infested with the isopod. For the first time, the ultrastructural features of L. redmanii in different growth stages were described, revealing the fine characteristics of the body appendages, the eyes, the antennae, and the antennules of the female, male, and juvenile isopod, as well as the external layers of the ova. Additionally, the detailed structures of the mouth parts, the sensory microtriches, and the male organs (penis, appendex masculine, and the genital furrow) were elucidated. A histological examination of the infested gill revealed damaged gill lamellae, leukocyte infiltration, and epithelial hyperplasia. Besides, microscopic examination of the skin showed focal erosion and periodic acid stain-positive foci in the dermis. Phylogenetic analysis revealed the close relationship between the L. redmanii isolated in this study and those recovered from mugiliid fry in the Mediterranean Sea in 2017. Based on our findings, we recommend using hatchery-reared fry instead of wild fry for supplying lakes and fish farms. Also, a strict biosecurity program must be implemented to avoid the transmission and spread of these disease-causing parasites.
Keywords: Common sole; Genetic characterization; Histopathology; Isopod; Livoneca redmanii; Ultrastructure.
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