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Chasmistes cujus

ListedMarch 11, 1967
FamilyCatostomidae (Sucker)
DescriptionOlive to blackish-brown sucker.
HabitatLakes; headwaters for spawning.
FoodBottom feeder.
ReproductionSpawns in the spring.
ThreatsDam construction, degraded water quality.


The cui-ui, Chasmistes cujus, is a is a plump, robust sucker, which attains a maximum length of about 25 in (64 cm) and a maximum weight of about 7 lbs (3.2 kg). It has a plump, robust body, and coarse scales. The head is large and blunt with small eyes. The mouth, atypical for a sucker, is oblique, rather than rounded, with thin lips and weak or nearly absent papillae. The cui-ui is pale olive to blackish-brown above, and white below. Breeding males have reddish sides. Females have a more bluish cast than males, attain greater length and weight than males, are more stocky in appearance, and have proportionally shorter fins. The female's vent becomes swollen and extended during spawning.


Spawning occurs once a year, primarily between April and late June, peaking in May. Temperature and flow characteristics of the Truckee River seem to determine timing of spawning, which occurs primarily at night in clusters of two to seven fish, most frequently with a female flanked on either side by a male. The demersal, adhesive eggs and sperm are broadcast over a large area. Males and females spawn repeatedly, often more than 100 times, each spawning act lasting three to six seconds. Males spawn actively over four to five days and females two and one-half to four days. There is no aggression among spawners and females spawn with different combinations of males.

Spawning has also been reported in Pyramid Lake at the entrance of freshwater streams on fine to coarse gravel and in the Marble Bluff fishway where the substrate is predominately compacted soil. Upstream migrating pre-spawning adults require pool environments, typically log jam pools, as refuge during the day.

The only migratory behavior reported for cui-ui involves adults ascending the Truckee River from Pyramid Lake to spawn, and their return to the lake and downstream migration of hatched larvae. Adults migrate to the south end of Pyramid Lake from late winter to early spring (February to May) where pre-spawning adults congregate off the mouth of the river. Young fish migrate downstream shortly after hatching, primarily from mid-May through mid-July, usually within about one month of peak adult migration.


The cui-ui spends its adult life in lakes and rivers and swims upstream in the spring to spawn.


The cui-ui was once plentiful throughout Truckee River and Pyramid Lake (Nevada); Klamath Lake and its tributaries (Oregon and California); and Utah Lake (Utah).

This species is now extremely rare or absent throughout its historic range. Although no population figures are available, the most viable remaining population of cui-ui appears to occur only in Pyramid Lake, Nevada. Adults migrate from Pyramid Lake up the lower Truckee River in spring to reproduce, and return to Pyramid Lake immediately following spawning. Larvae emigrate to Pyramid Lake shortly after hatching.


The natural habitat of the cui-ui has been drastically altered since the turn of the century by the construction of dams and water diversion channels. Water quality has steadily declined as flows decreased and the influx of silt and pollutants increased. Non-native fish species have preyed on cuiui young, significantly reducing the population.

The Cui-ui Recovery Plan, completed by the U. S. Fish and Wildlife Service (FWS) in 1992, has the stated objective of improving the status of cui-ui so that the species has at least a 0.95 probability of persisting for 200 years. This objective necessitates securing spawning habitat in the lower Truckee River and rearing habitat in Pyramid Lake as well as an avenue of passage for spawners and larvae.

The plan calls for restoring a portion of the Truckee River and Pyramid Lake to a natural and balanced condition. If a significant portion of this essential habitat can be reclaimed, the cui-ui stands a good chance of surviving. A captive breeding program is underway with the goal of restocking cuiui in Pyramid Lake.

Until April 1987, Nevada's Truckee River population was cut off from its spawning grounds at the river's headwaters. Then the Marble Bluff Fish Facility, designed to pass spawning fish of all types upstream past the Truckee River Dam, was opened. Almost immediately biologists observed a run of the endangered Lahontan cutthroat trout (Salmo clarki henshawi ) through the facility, soon followed by more than 4,000 cui-ui.

Continuing and future threats to the cui-ui include egg-hungry Lahontan redsides and alterations in the habitat, including channelization projects of the lower Truckee River by the Army Corps of Engineers, which have in the past resulted in the loss of protective cover, leaving many areas exposed to direct sunlight and solar heating.

Conservation and Recovery

In October 1996, the United States signed the Truckee River Water Quality Settlement Agreement with the cities of Reno and Sparks, Washoe County, the state of Nevada, and the Pyramid Lake Paiute Tribe. The agreement resolves litigation over approval and operation of the Reno-Sparks water treatment facility brought by the Pyramid Lake Paiute Tribe against Reno, Sparks, the state of Nevada, and the U.S. Environmental Protection Agency.

The FWS is preparing a wetlands management plan detailing actions necessary to best manage water being acquired to sustain 25,000 acres (10,117 hectares) of wetland habitat, including the timing of water applications to wetlands, and the volumes of acquired water to be applied.

In virtually the closing moments of the 101st legislative session in November 1990, Congress enacted a new law intended to help recover the cui-ui and Lahontan cutthroat trout and restore National Wildlife Refuge wetlands in Nevada vital to migratory waterfowl and shorebirds using the Pacific Flyway.

In addition to its progressive strategies for fish and wildlife, Public Law 101-618 confronts many long-standing water problems in the Truckee and Carson River basins of western Nevada: allocation of water between California and Nevada, coordination of water storage in Federal and private reservoirs, water management at one of the first Bureau of Reclamation irrigation projects, and resolution of certain Native American water rights disputes. Most significant for the conservation of endangered species and wetlands is a directive to acquire water rights expressly for fish and wildlife. The purchase of water at market rates should encourage the voluntary reallocation of water resources to benefit fish and wildlife in a manner that is equitable and most likely to enjoy local support.

Just as it addresses wetland restoration, Public Law 101-618 pursues the recovery of listed fishes in Pyramid Lake. In perhaps the most significant provision for these species, the Secretary of the Interior is directed to negotiate a formal Operating Agreement with the states of California and Nevada to govern management of the Truckee River reservoirs. Among other purposes, such an agreement may improve spawning conditions in the lower river through coordinated reservoir operations.


Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232


U.S. Fish and Wildlife Service. 1992. "Cui-ui Recovery Plan: Revision." U.S. Fish and Wildlife Service, Portland.