Population dynamics of the monogenean Anoplodiscus cirrusspiralis on the snapper, Pagrus auratus

Populations of Anoplodiscus cirrusspiralis were monitored for 1 year on tagged individual snapper in experimental cages kept in a large on-shore pond with flow-through filtered sea water. The cages were stocked with small and large fish at either low or high initial density. Irrespective of size and density, snapper with light initial infections maintained light infections, whereas fish with heavy initial infections showed fluctuations in parasite population size throughout the year. These data indicate that some snapper have an innate resistance to infection by A. cirrusspiralis, with little evidence for acquired immunity induced by heavy infection. Parasite longevity was greater on the pectoral fin than caudal fin, and greater on large than small fish irrespective of fish density; longevity was greater on susceptible fish than on resistant fish. Recruitment and mortality rates were greater on the pectoral fin and in low density cages, but were influenced by fork length.