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 the direction of body curvature. Regardless of morphotype, 98% of individuals were attached such that the convex side of the body was oriented towards the oncoming ventilating water currents. Further, 94% of individuals attached to the posterior faces of filaments leading to a predictable pattern of attachment for this species. Baseline concentrations of 12 blood parameters were determined for 30 fish species representing 12 families from Heron Island Reef, Great Barrier Reef, including P. leopardus (Serranidae), in addition to one estuarine species, the fork-tailed catfish Arius graeffei Kner & Steindachner, 1867 (Ariidae), from the Brisbane River. Baseline physiological status was determined via rapid blood sampling via caudal puncture of wild caught fish and analysis of a range of blood parameters. The validity of this method was evaluated via analysis of blood samples taken from hussar Lutjanus adetii (Castelnau, 1873). There were no significant changes in any of the measured blood parameters during the first two minutes following a stressful stimulus supporting the use of rapid blood sampling for baseline blood parameter determination. The measured baseline values provided a basis for comparison of post-stress values with differences between species in baseline and post-stress physiological condition discussed in relation to differences in lifestyle such as activity level and diet. Examination of the response of coral trout to hook-and-line capture over a 3-day period revealed an initial elevation of cortisol from a median baseline concentration of 0.40 nM (n = 17) to a peak of 19.01 nM (n = 7) 2 h post-hooking. Plasma osmolality, glucose and lactate also rose significantly and all parameters had returned to near baseline levels within 24 h of capture. Cortisol, glucose and lactate were identified as the best indicators of acute physiological disturbance in P. leopardus. Cortisol, glucose, lactate, osmolality and haematocrit were the best indicators of acute physiological stress in A. graeffei. An acute temperature increase of approximately 5oC over a period of 15 minutes was stressful to P. leopardus as indicated by an elevation of plasma cortisol. In contrast, an acute temperature drop did not have any significant effect on the physiological parameters measured. In an acute handling and air exposure experiment fish were rapidly hand-netted from holding tanks, subjected to a period of air exposure (0, 2, 4 or 6 minutes) and returned to the water for two hours prior to being blood sampled. Air exposure time did not significantly affect the resultant physiological parameters, suggesting that netting and transfer was the most stressful part of the experimental protocol. The potential commercial applications of these findings are discussed.
| Identifer | oai:union.ndltd.org:ADTP/253648 |
| Creators | Turner, Tracey Brooke |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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