Polyopisthocotylid Monogenean Infections of Amberjacks Seriola spp. in Japan

― Development of Zeuxapta seriolae (Monogenea: Polyopisthocotylea, Heteraxinidae) collected from Seriola dumerili was described and compared with that of Heteraxine heterocerca , the same heteraxinid species from Seriola quinqueradiata . Based on the morphology of the two monogeneans from very young with a symmetrical body to adult, specimens retrieved from the gills of cultured and wild Seriola spp. ( S. quinqueradiata , S. dumerili and S. aureovittata ) collected in Japan and its adjacent areas during 1975–2019 were identified. Heteraxine heterocerca , previously known only from S. quinqueradiata and S. dumerili , was also recorded from S. aureovittata , and Z. seriolae hitherto known only from S. dumerili and S. aureovittata , was recorded from S. quinqueradiata . As a result, both H. heterocerca and Z. seriolae were confirmed from all the three Seriola spp. Cultured S. quinqueradiata and S. aureovittata were often infected with both H. heterocerca and Z. seriolae , whereas wild Seriola spp. were infected with a single species of gill monogenean. Culture seeds of foreign origin should be monitored continuously, as information on the polyopisthocotylean monogenean infections of Seriola species known outside Japan is quite limited.