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Physiological and Genetic Factors influencing thermal tolerance in the Lahontan Cutthroat Trout (Oncorhynchus clarkii henshawi)
AuthorRobinson, Morgan Lind
AdvisorPeacock, Mary M.
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The Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) is one of sixteen recognized sub-species of cutthroat trout allopatrically distributed throughout the intermontane western United States. Threats to this subspecies include habitat fragmentation as well as competition and hybridization with non-native salmonids. Salmonids are adapted to cold-water conditions and water temperatures increased by anthropogenic activities limit the current distribution of native LCT populations. Fulton's condition factor K is a non-lethally estimated morphometric index used to evaluate the status of fishery stocks that involves the assumption that heavier fish of a given length contain more energy reserves in the form of body fat than those that weigh less. Data from a thermal challenge experiment with juvenile Lahontan cutthroat trout showed that high values of K were positively correlated with longer survival times. However, increasing body water had a greater positive effect on survival time as a similar increase in body fat or lean dry mass. Only body water was significantly correlated with K. These results indicate that fish with high values of K may not also have greater energy reserves in the form of fat. Most traits affecting fitness are determined by quantitative trait loci (QTL). QTL affecting upper temperature tolerance, growth rate, and disease resistance have been identified in salmonids. Survival time during a thermal challenge experiment revealed that this trait is variable and heritable in full sibling family groups of Lahontan cutthroat trout. Although no genetic linkage map exists for this species, loci associated with survival time were identified in this outbred group of hatchery-reared fish.