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The Colorado pikeminnow (Ptychocheilus lucius, formerly squawfish) is the largest cyprinid fish of North America and one of the largest in the world, with reports of individuals up to 6 ft (1.8 m) long[2] and weighing over 100 pounds (45 kg).^{[citation needed]} Native to the Colorado River Basin of the southwestern United States and adjacent Mexico, it was formerly an important food fish for both Native Americans and European settlers. Once abundant and widespread in the basin, its numbers have declined to the point where it has been extirpated from the Mexican part of its range and was listed as endangered in the US part in 1967, a fate shared by the three other large Colorado Basin endemic fish species: bonytail chub, humpback chub, and razorback sucker. The Colorado pikeminnow is currently listed as vulnerable by the IUCN.[1]

Colorado pikeminnow
Conservation status
Vulnerable  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cypriniformes
Family:	Leuciscidae
Subfamily:	Laviniinae
Genus:	Ptychocheilus
Species:	P. lucius
Binomial name
Ptychocheilus lucius Girard, 1856

Description

Like the other three species of pikeminnows, 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 9 rays. The pharyngeal teeth are long and hooked.

The reports of 6-ft individuals are estimates from skeletal remains, but a number of community elders, interviewed by the Salt Lake Tribune in 1994, reported that such individuals were once common. Catches in the 1960s ranged up to 60 cm for 11-year-old fish, but by the early 1990s, maximum sizes reached no more than 34 cm. Biologists now consider the typical size of an adult pikeminnow to be between 4 and 9 pounds, and reports of the fish lately exceeding 3 feet in length are now in question.

Biology

Young pikeminnows, up to 5 cm long, eat cladocerans, copepods, and chironomid larvae, then shift to insects around 10 cm long, gradually eating more fish as they mature. Once they achieve a length around 30 cm, they feed almost entirely upon fish.

This fish has an ontogenetic separation of life history stage. The altricial young 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 pikeminnows are potamodromous, making freshwater spawning migrations to home in on their natal areas. These migrations can begin as upstream or downstream movements, depending on the location of home range of individuals, and may involve 100 km or more.[3] 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 50–100 km downstream.[4]

Breeding

As talked about briefly in the biology section, Colorado Pikeminnow tends to spawn in late July, early August in the Green River. A clear indicator of when these fish tend to reproduce is when the water temperature reaches over 18° C. The fish as previously stated migrate towards deep pools and rushing water to lay their eggs. Once a female lays her eggs, male Colorado Pikeminnow will follow the trial of eggs, dispersing semen. These eggs hatch at different rates based on the temperature of the water. When the water is around 20° C, eggs hatched within 3-5 days, and at a higher temperature of 25° C, eggs hatched at around 2-3 days.[5] Along with the fast hatch rate, these eggs are also susceptible to movement. For example, looking at the Green River, one of a few remaining locations, eggs have been observed to move anywhere from 100 to 160 kilometers.[6]

Range

The species was once found throughout the Colorado Basin, so occurred in Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming, as well as in Mexico. Damming and habitat alterations have confined the species to the upper Colorado drainage; currently, remnant populations are known from the Green, Gunnison, White, San Juan, and Yampa Rivers. They have been transplanted to the Salt and Verde Rivers, both within their native range.

Threats

The Colorado Pikeminnow was once a species of fish that resided in much of the Colorado River Basin. Due to human impacts and the introduction of non-native fish species, the population has receded to the upper basin. According to the Native Aquatic Species Conservation in Arizona, the instillation of dams has altered the fish's movement.[7] Along with this, dewatering, altered stream flow, channel morphology, water quality, water chemistry, silt loads, and introduction of non-native fish have challenged the Colorado Pikeminnow (Sublette et. al. 1990, Muth and Snyder 1995). It has also been hypothesized that due to the installation of dams, the change in water temperature has altered breeding tendencies.[8] Breeding is water temperature dependent, meaning the temperature of the water must be perfect for spawning to occur. Changes in these conditions have caused breeding grounds to change. Non-native fish have posed a threat in both predation and competition for resources. With the introduction of various invasive catfish species, Greenback Cutthroat Trout, and red shiner (Cyprinella lutrensis), the population of Colorado Pikeminnow has declined drastically. In specific, a study was conducted analyzing the factors of recruiting young Colorado Pikeminnow. In particular, it was found that red shiners feed on the larvae of Colorado Pikeminnow in vivo.[9]

Population Reduction Efforts

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.[10] In September 1962, the Green River was poisoned beginning upstream of Flaming Gorge. The poison worked downstream for 3 days until it reached upstream of Dinosaur National Monument. Potassium permanganate was used to neutralize the rotenone, but concentrations were higher than expected and rotenone continued into the Dinosaur National Monument area.[11][12]

Restoration efforts

Recovery efforts are focused on operating dams to create more natural flow patterns, improving fish passage up- and downstream, and restricting stocking of non-native fish to reduce ecological interactions. In Arizona, hatcheries are in the process of restocking the Upper basin with Colorado pikeminnow. According to the Native Aquatic Species Conservation in Arizona, it was found that small fish could not avoid predation as well as the only successful site for reintroduction was the Green River, more specifically the upper Green river.[7] Fish up to 16 inches long have been released in the hopes of increasing the survival rate of the released Colorado Pikeminnow. There has been evidence that population numbers are increasing in the San Juan River.[7]

References

• William F. Sigler and John W. Sigler, Fishes of Utah (University of Utah Press, 1996), pp. 109–114
• USFWS Upper Colorado Endangered Fish Recovery Program
• USFWS Environmental Conservation Online System page for Colorado pikeminnow
• USFWS List of Fish Listed under Endangered Species Act
• Muth, R.T. and Snyder, D.E. 1995. Diets of young Colorado squawfish and other small fish in backwaters of the Green River, Colorado and Utah. The Great Basin Naturalist 55 (2): 95-104.

На других языках

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- [en] Colorado pikeminnow

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[es] Ptychocheilus lucius

Ptychocheilus lucius es una especie de peces de la familia de los Cyprinidae en el orden de los Cypriniformes.

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