What if I told you that there exists an apex predator fish in the lower rivers of the southern Rockies that grows as long as a man's leg -- with historical specimens recorded to six feet and a hundred pounds -- and that is capable of eating a mature trout without even thinking twice? And no, I'm not talking about Catfish, or even Pike and Tiger Muskies (none of which are endemic to the western US), though there is some pedigree in the name involved.
Ladies and Gentlemen, may I introduce the Colorado Pikeminnow (Ptychocheilus lucius), formerly known as the Squawfish. The largest Cyprinid fish in North America, which includes carp, Pikeminnows of various stripes used to inhabit the majority of the major river systems in the western United States, from the Columbia to the Colorado. 125 years ago they were considered prime food fish by the settlers, probably in no small part due the fact that a big one could provide a serious slab of fish steak for a dozen hungry rancheros.
According to Wikipedia, "Like the other... species of pikeminnow, it has an elongated body reminiscent of the pike. The cone-shaped and somewhat flattened head is elongated, forming nearly a quarter of the body length. Color grades from bright olive green on the back to a paler yellowish shade on the flanks, to white underneath. Young fish also have a dark spot on the caudal fin. Both the dorsal and anal fins typically have nine rays. The pharyngeal teeth are long and hooked."
While possessing no teeth in it's large terminally positioned jaws, Pikeminnow do have spikes in their throats that prevent prey from escaping backwards. Once a smaller fish is captured in the mouth of one of these voracious predators, there is no going back. After they reach a length of about a foot long, Pikeminnow become almost exclusively piscenovores, feeding on other fish and packing on weight at a rapid rate.
The species was listed as Endangered in 1967, the Colorado pikeminnow is currently listed as vulnerable by the IUCN. Ongoing efforts have been made at the state and federal level to restore the species, with have been met with limited success. In large part, this is due to a fundamental disruption in the ontogeny of the fish in regards to it's spawning cycle. The construction of major hydroelectric dams across the West in the first half of the last century provided impassible barriers for the Pikeminnow's spawning migration, much as impacted Pacific Salmon and Steelhead. but to a greater extent as Pikeminnow don't have the jumping abilities of Salmonids to successfully pass fish ladders.
Once dubbed "White Salmon", Pikeminnow have some of the longest migratory reproductive behaviors known in exclusively freshwater fish, with spawning occurring in headwater stream tributaries, but maturation and peak predation environments being in the lower mainstems of regionally principal rivers with significant depth and generally increased levels of sedimentation. This means that adult Pikeminnow will travel hundreds of miles to find perfect conditions for both the hatching of eggs and hunting grounds to support their potentially massive size.
While sportsmen with standard tackle sometimes target the species, it is discouraged in areas where reintroduction efforts are being made in the Colorado river basin. However -- and in apparent contradiction -- in the Pacific Northwest, bounties are offered to fisherman to present specimens of Northern Pikeminnow to fisheries agencies in attempts to eradicate the species in water where they could potentially cohabitate with, and prey on, juvenile salmon and trout. That Pikeminnow has managed to hang on by a thread despite all these man made assaults is remarkable.
While the new focus of fly fishing culture has expanded to include many new target species in both fresh and salt water, it remains to be seen whether a successfully restored population of Pikeminnow could -- or even should -- provide a sporting resource for fly anglers.