Effects of temperature on the repeat swimming performance, metabolic rates and swimming economy of salmonids (Oncorhynchus SPP.)

The primary goal of this research was to predict how changes in water temperature affect the swimming performance and energetic cost of transport in adult pink salmon (Oncorhynchus gorbuscha) and sockeye salmon (O. nerka), thus contributing to their ability to reach natal streams and spawn successfully. The prolonged swimming performance (U[sub crit]), minimum and maximum metabolic rate (Mo[sub 2-min] and Mo[sub 2-max]), oxygen cost of transport (COT) for upper Fraser River pink salmon were assessed across a range of naturally occurring temperatures using Brett-type swim tunnel respirometers and compared with values for sockeye salmon. To reduce mortality in senescing fish we minimized holding time and, therefore, thermal acclimation to as little as 48 hours before experiments. Therefore, we also used a salmonid model, the cutthroat trout (O. clarki clarki), to examine the effects of 48-hour and 3-week temperature acclimation periods on U[sub crit]. The length of the acclimation period had no significant effect on either the first or second U[sub crit] or on the recovery ratio (the quotient of U[sub crit-2]/U[sub Crit-1])- These results indicate that a 48-h acclimation to experimental temperatures may be sufficient in studies of swimming performance with this species. Contrary to previous beliefs, pink salmon were capable of similar relative critical swimming speeds as sockeye salmon (2.25 FL•s⁻¹), but sockeye salmon swam to a higher absolute U[sub crit](125.9 cm•s⁻¹) than pink salmon (116.4 cm•s⁻¹) because of their larger size. However, some individual pink salmon swam faster than all the sockeye salmon tested. Metabolic rate increased exponentially with swimming speed (P < 0.01) in both species and was higher for pink than sockeye salmon (P = 0.01), although swimming efficiency (was not significantly different between the species at their optimal swimming speeds minimum cost of transport; COT[sub min]) . The upper and lower limits of metabolism also increased exponentially with temperature (Mo[sub 2-min] P = 0.01; Mo[sub 2-max] , P < 0.01, respectively) but were not different between species (Mo[sub 2-min] P = 0.93; Mo[sub 2-max] , P = 0.38). The relationship between Mo₂ and swimming speed was positively affected by temperature in pink salmon (P = 0.01), but average and minimum COTs were independent of temperature over the range tested (9-22 ºC) in both species. Overall, a higher degree of inter-individual variability and thermal insensitivity in pink salmon suggest that this species might not be as locally adapted to particular upriver migrations as are sockeye salmon.Science, Faculty ofZoology, Department ofGraduat

Acclimatisation, de-acclimatisation and re-acclimatisation to hypoxia

World-wide, increasing numbers of individuals repeatedly alternate between low and high altitude for work and play. There is a general impression that acquired acclimatisation status persists for some time following return to sea level and that subsequent altitude tolerance is improved by previous hypoxic experience. However, it is unknown whether previous exposure to high altitude fundamentally alters the process of hypoxic re-acclimatisation (RA). My Doctoral research employed a number of approaches to investigate potential differences between the processes of initial acclimatisation (IA) and RA. The time course and mechanisms of hypoxic de-acclimatisation (DA) were explored to determine the time domains across which the retention of previous acclimatisation status might facilitate RA. Cross-sectional and longitudinal field studies were conducted to compare functional outcomes, cardiorespiratory function in rest and exercise and haematological responses throughout IA and RA in high-altitude trekkers. Results indicated that clinical outcomes and trekking performance were improved in RA but with limited physiological evidence of underlying improvements in hypoxic compensation. The haematological response to hypoxia was slightly greater in RA than IA, prompting further investigation of haematological RA in an animal model. Three paradigms of RA were used to examine the effect of IA and DA duration on the process of haematological RA in mice exposed to normobaric hypoxia. Despite altered erythropoietic control in RA treatments, the resulting haematological responses were generally consistent between IA and RA with no evidence of improved responses in RA. In fact, haematological acclimation was impaired in one RA treatment, possibly due to reduced availability of nutrients required for haemoglobin synthesis following an extended period of IA and upregulated erythropoiesis. Given the lack of physiological explanation for improved functional outcomes in RA, non-physiological mechanisms were pursued. Interviews with altitude-experienced individuals identified a perception that prior altitude experience leads to reduced altitude-induced anxiety and improved psychological tolerance of sensations associated with altitude exposure. Although physiological aspects of hypoxic re-acclimatisation merit further investigation, it is possible that improved psychological tolerance of high altitude contributes to the improved functional outcomes in RA that are reported here and elsewhere.Education, Faculty ofKinesiology, School ofGraduat