The physiological stress response of salmonids: considerations for field procedures and environmental monitoring

Investigating the physiological state of wild salmonids is challenging on many levels. The sensitive nature of an integrated physiological stress response directs how biological data is collected in the field and, consequently, how the results are interpreted. This thesis is comprised of two main components. The first component encompasses laboratory-based studies addressing the potential confounding effects of: 1) anaesthesia with either tricaine methanesulphonate (tricaine) or clove oil (eugenol) prior to blood/tissue sampling, and 2) capture by electroshocking, on the immediate and short-term responses of plasma/serum cortisol and glucose concentrations, haematocrit, plasma/serum lysozyme activity, and total leucocyte abundance in juvenile chinook salmon (Oncorhynchus tshawytscha). The second component involves a field-based exploration of the in situ physiological status, using the same five physiological traits, of wild bull trout (Salvelinus confluentus) in the Torpy River watershed, B.C., in relation to selected habitat attributes (stream gradient, discharge rate, and riparian canopy-closure). Anaesthetization and electroshocking did not significantly alter values for the five physiological traits provided that post-capture blood sampling occurred immediately. Tricaine and clove oil immobilization produced similar effects on the physiological stress response of juvenile chinook salmon. Clove oil (eugenol) shows promise as a viable and safe alternative to tricaine for aquacultural purposes and in laboratory- and field-based research. Electroshocking is an acute stressor from which juvenile chinook salmon can recover physiologically (usually within 12-24 h). Handling without shocking, however, significantly reduced serum lysozyme activity for up to 2 wks post-stress. Radiographs indicated that while some degree of spinal abnormality exists naturally in domestic chinook juveniles, individuals exposed to a single brief shock incur significantly more spinal deformities. Some of the variation in the stress physiology and non-specific immune function of wild bull trout in the Torpy River system were explained by the combined effects of stream gradient, discharge rate, and riparian canopy-closure. The physiological measurements of wild bull trout generally did not differ from those reported in the literature for other salmonid species. The "background" effects of these habitat features on the physiology of wild salmonids must be considered when interpreting field-collected data.