A Genetic Investigation of Suspected Redband Trout Populations

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Abstract
Samples from eight populations of native (presumably "redband") trout in Idaho from tributaries of the Owyhee River and adjacent streams flowing into the Snake River were analyzed by starch gel electrophoresis 1) to seek evidence of introgression from plantings of hatchery rainbow trout, 2) to determine the relationships among these populations, and 3) to identify the relationship of these populations to other "redband" trout from California, Nevada and Oregon. Average heterozygosities (range .048-.074) were well within the ranges reported for outbred rainbow trout populations suggesting that successions of severe "bottlenecks" had not occurred in these populations, in spite of the harsh environmental conditions. There was no evidence of hatchery introgression; rather, different measures indicated relationships based entirely on geographic variables with genetic similarity decreasing as linear stream distance increased. The native trout populations of Idaho were very similar to a population of native trout from Chino Creek, Nevada, in the Owyhee River drainage as well as to steelhead populations of the Snake River. Significant allelic frequency differences existed between the native Idaho populations and hatchery rainbow trout, coastal steelhead populations and "redband" trout native to southeastern Oregon and northeastern California. Morphological and physiological similarities to the latter group were hypothesized to be due to convergent characters or symplesiomorphically inherited characters. It was recommended that the term "redband" trout be retained to describe non-anadromous populations of rainbow trout adapted to harsh, arid environments, but that the term not necessarily infer taxonomic relationships among such populations.