Morphological and molecular characterization of Lernanthropus kroyeri, a copepod infesting the gills of European seabass Dicentrarchus labrax

The European seabass Dicentrarchus labrax, Europe's first commercially farmed non-salmonid fish and the most farmed Mediterranean fish, with Egypt as a major producer, is susceptible to several diseases, one of which being copepod infestation. Lernanthropus kroyeri (Beneden 1851) is a parasitic copepod that can be found across the Mediterranean Sea. Little research on L. kroyeri has been done along the Mediterranean Sea off the Egyptian coasts. In the current investigation, gill filaments, particularly those of the second-gill arch, were found to be infested with parasites with a prevalence rate of 23%. They were morphologically identical and confirmed as members of the family Lernanthropidae, having the characteristic features of L. kroyeri. Scanning electron microscopy (SEM) was used to examine morphological traits. Clinical and histological evidence of the parasite's catastrophic impact on infected fish has been described. DNA sequencing of the parasite's mitochondrial COI gene proved its identity, and it was the first of L. kroyeri to be added to the GenBank database, with the accession number MZ726776. The phylogenetic analysis revealed that the parasites arose from a monophyletic group that is distinct from other Lernanthropidae family members.