Concept
The greenback cutthroat trout (Oncorhynchus clarkii stomias) is the easternmost subspecies of cutthroat trout. The greenback cutthroat, once widespread in the Arkansas and South Platte River drainages of Eastern Colorado and Southeast Wyoming, today occupies less than 1% of its historical range. It is currently listed as threatened under the Endangered Species Act. It was adopted as the state fish of Colorado on March 15, 1994 replacing the unofficial rainbow trout. The greenback cutthroat's maximum size is . It has the largest spots of all cutthroats and is reported to have the most brilliant spawning coloration. Like all cutthroats, it has red coloration in the area of the lower jaw and throat. Historically, it has been reported to grow as large as . The cutthroat trout is thought to have evolved over the past two million years from other Oncorhynchus species which migrated up the Columbia and Snake river basins to the Green and Yellowstone river basins. Within the past 20,000 years, a population which crossed the Continental Divide during the most recent ice age gave rise to the greenback cutthroat. There is some controversy about the native range of the greenback cutthroat trout. It has long been thought that the greenback cutthroat was native to the South Platte and Arkansas River basins, likely due to the fact that the only surviving genetically pure population was found in a small creek in the Arkansas River basin. However, recent research has speculated that the greenback cutthroat was only native to the South Platte River basin, while the yellowfin cutthroat trout was native to the Arkansas River basin. Although it was common in the late 19th century, it began to decline when settlers arrived in the area. Mining in its native river basins led to sediment and toxic runoff in the water. These factors, along with water diversion for agriculture and overfishing, led to the decline of many greenback cutthroat trout populations. The introduction of non-native species such as brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (O.
