Serranid fishes are distributed around the world in tropical and warm temperate waters and are some of the most commercially important reef species. The 10 species of serranid fish of the genus Paralabrax Girard, 1856, are confined to the coasts of America, being located mainly in the Pacific Ocean, including the Gulf of California, with five of them occurring on both coasts of the Baja California peninsula, Mexico. A total of 278 fish of three species of Cabrillas of the Paralabrax genus [P. auroguttatus Walford, 193; P. clathratus (Girard, 1856) and P. nebulifer (Girard, 1856)] were obtained from various locations in the Gulf of California and the Pacific Ocean and were parasitized on lower pharyngeal plate and gills with a monogenean species of the Capsalidae family. The characteristic of the aseptate opisthohaptor is shared with the genera of four subfamilies: Entobdellinae, Nitzschi...