And from Wikipedia:
Cutthroat trout vary widely in size, coloration, and habitats. Though their coloration can range from golden to gray to green on the back, depending on subspecies and habitat, all populations feature distinctive red, pink, or orange marks on the underside of the lower jaw; usually the easiest diagnostic of the species for the casual observer. As adults, different populations and subspecies of cutthroat can range from 6–40 inches (15–100 cm) in length making size an ineffective indicator as to species.
Cutthroat will readily interbreed with the closely related rainbow trout, producing fertile hybrids commonly called "cutbow". Cutthroat will also hybridize with the O. gilae subspecies, the Gila trout and Apache trout.
source: http://en.wikipedia.org/wiki/Cutthroat_trout

