Abstract
A total of 60 specimens of the shore rockling Gaidropsarus mediterraneus from the coasts off Abu Qir landing site, Alexandria City, south-eastern Mediterranean Sea, Egypt. The collected fish samples were examined for metazoan parasites. Eight fish specimens (13.33%) were found to be naturally infected with one trematode species. The prevalence of parasitic infection increased to 20% during summer and fell to 6.66% during winter season. The recovered digenetic trematode was identified as Opecoeloides columbellae based on its morphological characteristics of an elongated body, presence of a ventro-terminal oral sucker, pedunculated acetabulum with papillae, glandular cells in the lateral pharyngeal region, presence of an accessory sucker, two tandem and oval-shaped testes, tri-lobed ovaries, four vitelline ducts anteriorly to the ovary, absence of a cirrus pouch, ceca opened into the excretory vesicle, and presence of uroproct. Molecular characterization was carried out based on partial sequencing of the ITS-1 gene region to determine the taxonomy of this opecoeloid parasite based on its morphology. It was found to have a close identity of up to 74% with other species retrieved from GenBank. Phylogenetic analysis of the parasite sequences in conjunction with existing data showed that this opecoeloid species belongs to the Opecoelidae family within Allocreadioidea. This species was found to be deeply embedded in the Opecoeloides genus with close relationships to the previously described Opecoeloides species (gb vertical bar KX594823.1, and KX594822.1) with strong nodal support value in the same taxon. (C) 2019 Published by Elsevier B.V.