The Colorado pikeminnow, known by its scientific name Ptychocheilus lucius, was formerly called the Colorado squawfish. It is the largest cyprinid fish of North America and one of the largest in the world, with past reports of individuals up to 6 feet and weighing over 100 pounds. It was once plentiful on San Bernardino County’s eastern coast but rarely makes that far down stream anymore. It was .an important food fish for both Native Americans and European settlers. It is endemic to the Colorado River and like three other Colorado River endemic species – the bonytail chub, the humpback chub, and the razorback sucker – its numbers and range long ago declined to the point where it was listed as endangered. That listing came in 1967, and at this point it is considered vulnerable by the International Union for the Conservation of Nature.
All four species of pikeminnow, including the Colorado River variety, have elongated bodies similar to the pike. It has a cone-shaped and somewhat flattened and elongated head which accounts for close to one-fourth its 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. Its pharyngeal teeth are long and hooked.
Colorado pikeminnow can live up to 40 years.
The reports of six foot long Colorado squawfish are estimates from skeletal remains. Anecdotal accounts hold that such individuals were once common. Catches in the 1960s ranged up to 25 inches for 11-year-old fish but, by the early 1990s, maximum sizes reached no more than 14 inches. Biologists now consider the average size of an adult pikeminnow to be between 4 and 9 pounds, and reports of the fish latterly exceeding 3 feet in length are now in question.
Young pikeminnows, up to two inches long, eat cladocerans, copepods, and chironomid larvae, then shift to insects at around four inches, gradually eating more fish as they mature. Once they achieve a length of about one foot, they feed almost entirely upon fish.
The young fish emerge from whitewater canyons, enter the drift as sac-fry and are transported downstream. Habitat for the young fish is predominately alongshore backwaters and associated shorelines of more alluvial reaches of the turbulent and turbid rivers of the Colorado system. In contrast, adults reside in more well-defined channels, where they seek eddy habitats and prey on suckers and minnows. Colorado pikeminnow make freshwater spawning migrations to their natal areas. These migrations can begin as upstream or downstream movements, depending on the location of home range of individuals, and may involve 60 or more miles. Spawning occurs around the summer solstice, with declining flows and increasing temperatures. Breeding males are bronze-colored and heavily covered with tubercles while females are generally larger, lighter in color and with fewer tubercles. As the fish reach the spawning location they stage in deeper pools and eddies and make spawning runs into nearby runs and deep riffles, where the adhesive eggs are released. Upon hatching and swim-up the small fry are entrained and carried 30 to 60 miles downstream.
The species was once found throughout the Colorado basin, so it occurred in Arizona, California, Colorado, Nevada, New Mexico,Utah, and Wyoming, as well as in Mexico. Damming and habitat alterations have decimated the fish’s populations. Additionally, land managers in the past have attempted to reduce the native fish population of the Colorado basin in favor of sport fishing. In the mid-1960s, the federal government poured the poison rotenone into the Green and San Juan Rivers, attempting to create an environment supportive of non-native sportfish. They have been transplanted to the Salt River and Verde River, both within their native range.
Recovery efforts are focused on operating dams to create more of a natural flow pattern, improving fish passage up- and downstream, and restricting stocking of nonnative fish to reduce ecological interactions. Thus far, progress in recovering the pikeminnow has been limited.