In this study, we compared seasonal changes in the number of the monogenean parasite Benedenia seriolae infesting amberjacks: yellowtail Seriola quinqueradiata, goldstriped amberjack S. lalandi and their hybrid, i.e. yellowtail _??_ ×goldstriped amberjack _??_ (termed as YG) . These fish, individually identified by passive radio frequency transponder tag and kept in a single net cage throughout the experiment, were examined individually for the intensity of infection. All the fish groups showed similar seasonal changes in the intensity of infection; the number of parasites peaked in June (29-237 per fish), while it was low in March, September and October (0-18 per fish) . Goldstriped amberjack was most heavily infected, followed by YG, and then yellowtail. When compared within each fish group, there was a big difference in the intensity of infection among individuals. These results suggest that the susceptibility against B. seriolae infection is different not only among fish species, but also among individuals within the same fish species.
