Largemouth bass ( <i>Micropterus salmoides</i> , Lacépède, 1802) infestation by <i>Ergasilus sieboldi</i> (Nordmann, 1832) in Southern Italy

Ergasilus sieboldi are parasitic copepods belonging to the Ergasilidae family. They affect the gills of various freshwater and marine fish, causing mortality events worldwide. Like other copepods, E. sieboldi adult females are parasitic; while, the adult males die after fertilisation. Lesions caused by these parasites can create prerequisites for secondary infections by other pathogens, such as bacteria, viruses and fungi. This study aimed to describe the first case of E. sieboldi in largemouth bass (Micropterus salmoides) in Italy. Morphological analysis identified the genus of copepods collected from gills, distinguishing them from Neoergasilus, already described in Italy. The species was identified with molecular characterisation and phylogenetic analysis based on 28S rDNA sequencing. Histopathological analysis of the gills highlighted damage to the gill lamellae such as erosion, necrosis and desquamation typically caused by ergasilids.