Juvenile Atlantic salmon (Salmo salar) in Tasmanian aquaculture facilities routinely experience large variations in holding temperatures, indoor tanks are held at 16oC while the fish in outdoor holding pools can be exposed to summer temperatures of up to 24oC. During periods of anthropogenic disturbance, fish activity increases and with it their oxygen consumption, which rapidly drives the dissolved oxygen level in their holding tanks down to approach hypoxic conditions. It was hypothesised that exposure to heat and/or hypoxia during parr development would impair successful smoltification in response to their transfer to seawater The research in this thesis was conducted to (i) establish whether the metabolic characteristics of the geographically and genetically isolated Atlantic salmon population in Tasmania had different physiological and biochemical responses to elevated temperature from those recorded for populations in the Northern Hemisphere; and (ii) whether early exposure to heat and/or hypoxia resulted in failed smolts, after seawater transfer. Initially, a series of experiments were undertaken to examine the effect of environmental stress, on metabolic characteristics, condition factor and coping style of these fish, in response to a) elevated temperatures, b) progressive hypoxia and c) periods of confinement prior to respirometry. Subsequently, the effect of elevated rearing temperature on parr readiness to smolt was examined.