The common coral trout Plectropomus leopardus (Lacepède, 1802) is an important commercially and recreationally fished species in Australia. This thesis examined a number of factors that may affect the suitability of this species for aquaculture including ectoparasite fauna and stress physiology. Examination of the ectoparasite fauna of P. leopardus revealed one new species, Hatschekia (Species A), and new host records for the copepods Peniculisa bellwoodi and Sagum epinepheli. Other ectoparasites recorded included Dissonus manteri, Hatschekia plectropomi, Lepeophtheirus plectropomi, Dentigryps litus, Trochopus plectropomi, Diplectanum plectropomi, Aega lethrina, Argathona macronema and turbellarians. There were significant differences between the ectoparasite communities of P. leopardus from Heron Island Reef and a population from the Cairns region of the Great Barrier Reef with absence of some parasites from certain sites and variations in the intensity of infection of other parasites. Dissonus manteri, H. plectropomi and P. bellwoodi were associated with the most severe pathology as determined by gross examination, histology, scanning electron microscopy and vascular casting techniques. This pathology was considered unlikely to cause a significant threat to host fish survival at the infection intensities observed on wild fish. This hypothesis was supported by the observation that levels of ectoparasite infection of wild fish were insufficient to initiate a stress response, as determined by blood parameter analysis. Detailed examination of the distribution of H. plectropomi on the gills of P. leopardus revealed a site preference for holobranchs 2 and 3. Filaments near the ends of gill arches and those around the bend in the gill arch were rarely occupied. The chance of coming into contact with a suitable attachment site along with the ability to withstand ventilation forces at that site may be the major factors affecting the distribution of this species. Two H. plectropomi morphotypes were identified based on ...