The Effects of Domestication and Temperature on Growth and Swim Performance in Clonal Lines of Rainbow Trout, Oncorhynchus mykiss

Thesis (Ph.D.), Washington State UniversityIn the western U.S., the Pacific salmonids (Oncorhynchus spp.) are of significant cultural, socioeconomic and ecological importance. However, despite decades of conservation efforts, their continued decline remains a great concern. Two critical factors impacting the sustainability of salmon and steelhead populations in the Pacific Northwest include genetic introgression of captive-reared hatchery fish and climate warming. Although salmonid hatcheries have been recognized as having a valuable role in restoring wild stocks, gene flow from domesticated hatchery fish into wild populations presents obstacles for conservation. Additionally, climate change is predicted to continue to increase stream temperatures in the Pacific Northwest, which is particularly hazardous for cold-water dependent Oncorhynchus spp., as their physiology, behavior, and distribution are crucially linked to temperature. Here these factors were investigated using clonal lines of rainbow trout (Oncorhynchus mykiss) by evaluating phenotypic responses to these two factors in the context of developing management protocols to facilitate their sustained existence.In the first two chapters the effects of hatchery selection for body size and increased temperature on growth and sprint swimming speed were examined; both of these measures represent components of evolutionary fitness in fish. In Chapter One, the effect of increased size selection on growth and sprint speed at a constant temperature of 15°C was examined by repeatedly measuring these traits over a period of ten weeks in clonal lines derived from both wild and captive-bred source populations. In Chapter Two, the effect of temperature was tested by repeatedly measuring growth and sprint speed over ten weeks in clonal lines originating from Alaska, Oregon, and California held at two different temperatures, 10°C and 18°C. In both of these chapters, we observed results that may suggest a tradeoff between increased body size/growth rate and reduced (slower) sprint speed. In Chapter Three we incorporated this tradeoff into a mathematical model to better understand their evolutionary and ecological consequences on populations of wild salmonids. We conclude that using hatchery fish with characteristics most similar to wild fish render the greatest possible chance of successful supplementation.Zoology, Washington State Universit