The cui-ui, Chasmistes cujus, is a large sucker fish endemic to Pyramid Lake in northwestern Nevada. It feeds primarily on zooplankton and possibly on nanoplankton (such as algae and diatoms). The maximum size of male cui-ui is approximately (21 in) and (3.5 lb) while females reach approximately (25 in) and (6 lb). The life span of cui-ui is typically about forty years, but the fish do not reach sexual maturity until at least age eight. The cui-ui is not only a critically endangered species, but is also one of the few surviving members of its genus.
The cui-ui population is generally improving in numbers, having attained an estimated population exceeding one million in 1993, thanks to the efforts of the U.S. Environmental Protection Agency in analysis of the Truckee River spawning grounds and of the Nevada Department of Environmental Protection and EPA in following up on protection measures. The reason the cui-ui remains critically endangered is the recent history of recruitment variation, illustrating that in many years of the 1970s and 1980s there was virtually no recruitment whatsoever due to unsuccessful spawning in an unfavorable water quality and water flow environment of the Truckee River.
Paiute tribe and the Cui-ui
The Pyramid Lake band of Northern Paiute called themselves the “Cuiyui Ticutta”, which means cui-ui eaters. Together with the Lahontan cutthroat trout the cui-ui was an important food supply for the Cuiyui Tikutta and neighboring Paiute bands who would travel to Pyramid Lake to share in the harvest during the spring spawning runs. Subsequent to white settlement of western Nevada in the 1860s many Cuiyui Ticutta made a living by selling fish, although the whites generally preferred trout to cui-ui. Cui-ui were also still important for subsistence.