Morphological and Molecular Identification of Hysterothylacium Larvae (Nematoda: Raphidascarididae) in Marine Fish From Tunisian Mediterranean Coasts

Abstract

The taxonomy ofHysterothylaciumgenus in Mediterranean waters remains incomplete and unresolved. The aim of the current study was to investigate the morphological and molecular identification of selected species ofHysterothylaciumlarvae in marine fish from the Tunisian Mediterranean coasts. A total of 192 marine fish samples were examined. In total, thirty-seven third-stage larvae ofHysterothylaciumwere morphologically identified asHysterothylaciumtype V. In the present study, representatives of this type from the Mediterranean Sea were genetically characterized for the first time by sequencing the rDNA ITS (ITS1-5.8S-ITS2) regions and mtDNAcox2gene. This study represents the first report ofHysterothylaciumtype V from the Mediterranean Sea. We also reportMullus barbatus,M. surmuletus, andPagellus erythrinusas new hosts for this larval type. Based upon molecular and phylogenetic analyses considering the rDNA ITS regions, theHysterothylaciumtype V described here was classified as a new genotype, named Genotype B. The valid genetic data of the describedHysterothylaciumtype V in the present study can be used to establish the phylogenetic relationships amongHysterothylaciumspecies from the Mediterranean Sea and worldwide for future research.