Morphological identification and molecular characterization of 18S rDNA of two hemiurid trematodes (Lecithocladium cristatum Rudolphi, 1819 and Lecithocladium parviovum Yamaguti, 1953) infecting the greater lizardfish Saurida tumbil (Pisces: Synodontidae) inhabiting the Red Sea.

A total of 100 specimens of the greater lizardfish Saurida tumbil were collected during the current investigation from the coasts of Hurghada City at the Gulf of Suez, Red Sea, Egypt; and necropsied to study their metazoan parasites. Of the total specimens collected, 32.0% were found to be naturally infected with hemiurid trematodes. The prevalence of parasitic infections increased to 48.0% during winter and fell to 16.0% during summer season with no mixed infections being observed. Two species of the hemiurid trematodes were recovered from the stomach of the infected fish samples; both belonged to the genus, Lecithocladium, in the family Hemiuridae. The morphometrics of their different body parts were characterized by light microscopy. Comparisons between the recovered parasites and previously studied species showed that the present investigation is the first report of Lecithocladium species infecting marine fish in the Red Sea. Additionally, molecular analysis of the parasites' 18S small subunit (SSu) rDNA was performed to determine their phylogenetic position in relation to previously recorded species in GenBank, which distinctly supported the morphological characteristics identified here. Two hemiurid species from the genus, Lecithocladium, to be L. cristatum and L. parviovum, were identified. Comparison of 18S rDNA sequences revealed that they had 98.0% sequence identity with L. excisum (gb| AJ287529) with a low divergence value. On the basis of these results, the two species isolated here were recorded within a new host and locality records in Egypt.