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16 Colorado Region This region in Nevada contains a diverse native fish fauna that inhabits both river and spring systems. Fishes are currently distributed throughout seven (7) valleys along the central and southeastern margin of the state. Specific commentaries follow the order given in Table 3• Catostomus latipinnis: Flannelmouth Sucker This species inhabits portions of the Virgin River along the extreme south- eastern portions of the state. Its main distribution in the river occurs in Utah and the Arizona strip, but it is found in reduced numbers in the lower reaches near Mesquite, Nevada. This species has been impacted in recent years by agricultural diversions and habitat modifications. The Virgin River is only one of several systems that this animal is found in, so no recommendations are made at this time. Crenichthys baileyi: White River Springfish This species has just been recently designated into several subspecies by Williams and Wilde and will be treated accordingly in this text. C. baile i ssp.: Moapa White River Springfish This subspecies is confined to the headwaters of the Moapa River approxi- mately 9 miles west of Glendale, Nevada. It has experienced several population declines since the introduction of Gambusia affinis in the 1930's and Poecilia mexicana in the early 1960's. Field collections in 1978-79 indicate that they are stabilizing and have increased somewhat since these early periods. The habitats continue to be modified for agricultural purposes, and exotics are presently in high numbers. The continued withdrawal of ground water in this area for power plant usage and the MX missile system may lead to loss of habitat. It is recommended that this species be listed as of special concern. C. bail yi ssp.: Hiko White River Springfish This subspecies was known from two locations in Pahranagat Valley, Hiko and Crystal Springs. The former population was extirpated in the 1960's by bass. The remainirig population at Crystal Springs has been severly reduced in numbers by the presence of Cichlasoma nigrofasciatum and other exotic species. This species should be listed as of special concern or threatened, and steps to eliminate or control exotics should be initiated. C.b. bailgyri: White River Springfish This subspecies is confined to Ash Springs, Pahranagat Valley. It is currently being heavily impacted by the presence of exotic species such as Cichlasomq nigrofasciatum and Poecilia mexicana. C.b. baileyi is considered to be rare in this locality as of fall 1979. This subspecies should be considered as endangered and steps taken to rehabilitate the habitat. C. baileyi ssp.: Preston White River Springfish This subspecies inhabits those springs in the northern extremity of White River Valley adjacent to Preston and Lund. All of these habitats currently contain one or more exotic fish species and have reduced populations. The proposed deployment of the MX missile in this valley could seriously reduce numbers and/or cause the loss of habitat. It is recommended that this animal