SPATIAL AND TEMPORAL VARIATION IN POPULATIONS AND COMMUNITY OF ECTOPARASITES ON YOUNG SNAPPER, PAGRUS-AURATUS (BLOCH-AND-SCHNEIDER) (SPARIDAE), FROM THE WILD AND CAPTIVITY AT PORT-HACKING, SYDNEY, AUSTRALIA

Snapper in both the estuary (0+, 1+ age classes) and from offshore ree fs (1+, 2+, 3+ age classes) at Port Hacking, NSW, were infested with t he monogeneans Lamellodiscus pagrosomi, Anoplodiscus cirrusspiralis an d Bivagina pagrosomi and the copepods Unicolax chrysophryenus, Pseudoe ucanthus australiensis, Hatschekia pagrosomi, Clavellopsis sargi and L ernanthropus atrox; offshore snapper also had the monogenean Choricoty le australiensis and the copepods Caligus spp, and Lepeophtheirus seki i. Most species had a higher prevalence, but not intensity, on offshor e fish. Season was not a significant factor for most infrapopulations. Species richness, number of parasites and diversity were greater on o ffshore fish and differed among estuary samples but not offshore sampl es. Estuary infracommunities were dominated by L. pagrosomi (mainly 1) and B. pagrosomi (mainly 0+); C. sargi and L. atrox dominated when r ichness was low. Offshore infracommunities were dominated by H. pagros omi except in winter when L. pagrosomi was dominant, possibly owing to movement of estuary fish to offshore reefs. Captivity in experimental cages in the estuary resulted in transient increases in A. cirrusspir alis, B. pagrosomi and Benedenia sekii. Lamellodiscus pagrosomi increa singly dominated all samples and infracommunities. Neither condition f actor nor stocking density had a significant influence on infestation.