Aren’t cutthroat and rainbow all just the same? Are there really any differences other than the little gash on the throat of the cutthroat or the iridescent stripe on the rainbow? Those who have never, or do not regularly, catch rainbow and cutthroat trout may have those questions.
Even more frequent questions, are: Aren’t all cutthroat trout the same? They’re just called different names based on where they are located, but they are actually all just “cutthroat” and no subspecies, right?
The answer to each of the above questions is, “No!”
There are three main ways to field test if you have a cutthroat trout (as opposed to some other type of trout, typically rainbow). These apply for almost all species, although it does get a bit dicey when dealing with the redband rainbow trout (they may display many of these cutthroat characteristics): 1) the throat markings (yellows, oranges and reds in coloration), 2) basibranchial teeth (teeth on the tongue, toward the rear of the tongue) and 3) a maxillary (the “mustache”) that extends well past the eye.
At this point it might be a good idea to diverge for a moment. Most knowledge we have today of cutthroat trout comes from the work of Dr. Robert Behnke and his students. There are some critics of some of his methods, but overall, there is overwhelming agreement with his methods.
There are other tests which can be done in more of a laboratory setting. Some of these tests deal with counting certain features of the fish (called merisitic characters—this is the area of most contention with Behnke’s work), such as the number of: scales in the lateral line and above the lateral line, vertebrae, intestinal pyloric caeca, rays in the pelvic (and other) fin, and gill rakers.
Newer methods involving DNA have also been employed, both on the chromosomes and mitochondria. Most of these tests confirm Behnke’s merisitic work.
The historical distribution of cutthroat trout are from northern Mexico in the south to southern Alaska in the north. From the Pacific coast in the west to a line connecting eastern Montana to eastern New Mexico on the east. The following is a good map of that range: http://www.westerntrout.org/trout/maps/historic/historic_ranges.jpg
You can find more information about some of the subspecies at the Western Native Trout Initiative.
The best current information regarding cutthroat trout is the excellent (highly recommended) book, Cutthroat: Native Trout of the West, by Patrick Trotter, 2nd edition, 2008 by the University of California Press.
The following illustrations were mostly from the Western Native Trout Initiative at http://westernnativetrout.org/content/what-are-western-native-trout/ and from various internet searches.