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These are technically non-dominant traits---they are recessive traits. Furthermore, the slash is ironically a non-definitive for cutthroat trout. The orange slash can pop up in rainbow trout populations with no contact with cutthroat trout (the gene would have to be present in rainbow trout in order for them to produce viable offspring), but it does serve as a good indicator if coupled with any of the primary characteristics. The primary physical taxonomic features that define a cutthroat trout are basibranchial teeth (little teeth-like protrusions on the tongue) and jaw that extends past the eye orbital. The most reliable secondary characteristic is the spotting pattern---higher density near the tail. Although, this characteristic can be easily washed out of cutthroat population (like those in the Oldman drainage). In this case, the jaw clearly extends beyond the eye. The secondary characteristic of increased spotting near the tail is also present. And, of course, the orange slashes are present. Spotting pattern extends to the head, but not a reliable marker. If there were basibranchial teeth, you might have close to a pure cutthroat. Almost all Alberta populations of cutthroat have been hybridized to some degree with rainbow trout, so technically almost every cutthroat is a cuttbow. I think the only 'pure' populations are in a couple lakes in the Banff park. source: wife is trained taxonomist and practicing biologist. EDIT: It has been pointed out to me, and I was scolded by my wife, that there are several statistically genetically pure pockets of cutthroats. Still it is estimated that approximately 70% of the known populations have been interbred with rainbow trout.