Cutbow

The cutbow (Oncorhynchus clarkii × mykiss) is an interspecific fertile hybrid between rainbow trout (Oncorhynchus mykiss) and cutthroat trout (O. clarkii). While natural separation of spawning habitat limited hybridization in most native populations of rainbow and cutthroat trout, introduction of non-native hatchery-raised rainbow trout into native cutthroat trout range increased hybridization across the landscape. Due to these introductions, many populations of cutthroat trout are at risk of genetic pollution. As a result, significant management intervention at state and federal levels has occurred to preserve native populations of cutthroat trout.

History
Cutbow can occur naturally (albeit irregularly) where the native ranges of both parent species overlap, such as between coastal rainbow trout (O. mykiss irideus) and coastal cutthroat trout (O. clarkii clarkii) and between Columbia River redband trout (O. mykiss gardineri) and westslope cutthroat trout (O. clarkii lewisi). . However, early stocking of rainbow trout in watersheds that contained native cutthroat trout throughout the 19th and 20th centuries increased the occurrence of cutbow in North America. Increased hybridization imperiled or extirpated many populations of cutthroat trout, and hybridization was recognized as problematic by early North American ichthyologists and fishery scientists.

Description
Like most fish hybrids, cutbow are difficult to identify based on external characteristics alone. This is further complicated by phenotypic variation of cutthroat trout across their range. Subsequently, many anglers confuse cutbow with rainbow or cutthroat trout. Cutbow have reddish or orange slash markings under the jaw like cutthroat trout. Though most cutbow have dots on their bodies, patterns vary between each fish.

Reproduction
Cutbows are created when the female cutthroat trout's eggs are fertilized by a bigger male rainbow trout. Cutbows spawn during spring and prefer temperatures between 40 and 50°F. They are able to reproduce in natural habitats and in hatcheries. They are almost immune to whirling disease, which affects most trout in Colorado.