Arid Lands of the Southwest 

Fish communities within a 

desert spring or stream often 

consist of only a few genetically 

unique species such as desert 

pupfish (Cyprinodon 

macularius), Moapa dace 

(Moapa coriacea), and cui-ui 

(Chasmistes cujus) with 

adaptations particularly suited 

for their natural environments. 

Today, these fishes are in

jeopardy mainly due to several 

anthopogenic effects. Perhaps 

the greatest threat is man's 

constant need for water and his 

manipulation of the natural 

environment via diversions of 

surface water and the mining of 

groundwater. Without a reliable 

water source, many native 

fishes in arid lands are in 

constant danger of perishing. 

Another important 

anthropogenic factor is the 

introduction of nonnative fishes 

into these simple ecosystems. 

Through still poorly 

understood ecological 

interactions, nonnative species 

often replace the unique 

native species. Desert fishes 

may be especially vulnerable 

to invasions of nonnative 

fishes because they generally 

evolved under conditions of 

little or no competitors and 

predators. 

A third anthropogenic effect is 

contamination by metals, 

pesticides, and other chemical 

compounds that cause outright 

lethality or sublethal effects, 

such as reproductive 

impairment, reduced growth, 

increased vulnerability to 

environmental stresses and 

disease, and behavioral 

changes. Because arid 

ecosystems are already very 

fragile, any of these 

anthropogenic disturbances can 

lead to extinction of native fish 

species. To avoid irreversible 

ecological catastrophes, people 

must be made aware of how 

their actions can adversely 

affect native fishes and other 

aquatic biota in arid lands. 

Desert Pupfish are Losing 

Ground

The desert pupfish is one of a 

small handful of native fishes 

U.S. Department of the Interior WFRC Fact Sheet 

U.S. Geological Survey August 11, 2005 

Agricultural drain in the Salton Sea Basin. 

When thinking about plants and animals that 

inhabit hot arid lands of the southwestern U.S., 

fish are easily overlooked by most people. 

However, these desert lands often contain 

isolated springs or cienegas (a Spanish term 

referring to permanently saturated "seep 

wetlands") and streams supporting native fishes 

that occur no where else in the world. These 

aquatic remnants from the last Ice Age have 

survived for thousands of years due to an 

amazing ability to tolerate harsh environmental 

conditions, especially extremely high water 

temperatures, high salinities, and unpredictable 

water flows.
Desert pupfish collected

from an agricultural drain

adjacent to the Salton

Sea. These fish are 

measured and weighed,

then released at the 

collection site. 

View of Salt Creek near its terminus with the Salton Sea 

(view is looking upstream). Desert pupfish inhabiting this 

reach are occasionally eliminated during summer when the 

creek dries up, but recolonization occurs from the sea when

high winter flows breach a barnacle bar that typically blocks

its mouth. 

that still persist in the arid 

Southwest. Although 

previously widespread 

throughout the Sonoran and 

Mojave deserts of southern 

California, southern Arizona, 

and northwest Mexico, this fish 

is now confined mostly to 

artificial refugia and a few small 

streams. Perhaps the largest 

population occurs in agricultural 

drains that flow into the Salton 

Sea. Plummeting numbers of 

pupfish throughout its historical 

range led to the listing of this 

species for federal protection as 

endangered in 1986. 

Recent studies by the USGS 

Western Fisheries Research 

Center (WFRC) have shown 

that predation by nonnative 

fishes may have a major 

influence on abundance and 

distribution of pupfish in and 

around the Salton Sea. As a 

result, resource managers have 

recommended eliminating 

nonnative species to preserve 

remaining pupfish populations. 

Today, natural habitats for 

pupfish include San Sebastian 

Marsh and San Felipe Creek on 

the southwestern edge of the 

 

The Moapa dace is a

member of the 

Cyprinidae family

and the only

member of the 

genus Moapa. This 

species has a

distinctive leathery

appearance, hence 

the name coriacea. 

The Moapa dace can

grow to 5 inches in 

length, and is 

omnivorous. 

Salton Sea, and Salt Creek on 

the northern shore. 

Pupfish can tolerate hostile 

environments with excessively 

high temperatures, high 

salinities, and low dissolved 

oxygen, which enable them to 

survive in environments hostile 

to less hardy nonnative species. 

They generally do not live 

beyond 2 years of age. 

Breeding males are territorial 

and acquire an intense blue 

coloration to attract mates. 
quantity and quality through 

loss of water volume that 

reduces the extent of thermal 

habitat on which the fish is 

dependent. 

Biologists from the WFRC were 

contracted by the U.S. Fish and 

Wildlife Service to collect 

pertinent data and develop a 

model that predicts the 

persistence of Moapa dace 

under various changing 

environmental conditions. This 

new generation model, along 

with field and laboratory data, 

will include movement, growth, 

and respiration of the fish, and 

will be a useful tool to manage 

and protect Moapa dace in its 

changing environment. 

Unique Warm Water Fish Get 

Help 

The Moapa dace is an 

endangered fish species that 

occurs only near the origin of 

the Muddy River which 

originates from warm water 

springs, about 50 miles 

northeast of Las Vegas. These 

small fish live in water with 

temperatures ranging from 26 to 

32o

 C [79 o F to 90 o F] – such 

fish are called “thermal 

endemic” species, meaning that 

they require warm water to 

survive. 

The persistence of the Moapa 

dace has recently been 

jeopardized. First, the 

headwaters of the Muddy River 

were invaded by nonnative blue 

tilapia (Oreochromis aureus), 

which are known herbivores but 

switch to eating dace once all 

the aquatic vegetation was gone, 

and eliminated Moapa dace 

from 90% of its former range. 

Secondly, spring flow in 10% of

the habitat not invaded by blue 

tilapia is declining due to

pumping of nearby groundwater 

(the carbonated aquifer), the 

source of the spring flow. 

Reduction in spring flow is 

expected to lessen habitat 

In the 20th century their river spawning migration was 

blocked by agricultural water diversions, the largest of

which is the transbasinal canal (Truckee Canal) that 

diverts water to the Carson River system and thence to 

the Carson Valley. Completed in 1906 as part of this 

Nation’s first Bureau of Reclamation Project (The 

Newlands Project), the diversion was largely 

responsible for causing Pyramid Lake to subside 

roughly 80 feet, creating a shallow impassable delta at 

the mouth of the Truckee River. 

Cui-ui (Chasmistes cujus) 

Pyramid Lake, Nevada

Saving an Old Fish in the 

Desert 

The cui-ui (pronounced “Kweewee”) is a sucker that occurs 

only in Pyramid Lake, Nevada. 

It reaches lengths in excess of 

30 inches and weights up to 10 

pounds. Cui-ui are a favorite 

food fish of the Northern Paiute 

Indians and have special 

cultural significance to the tribe.

Cui-ui are obligatory lake 

dwellers that spawn in the 

Truckee River, Pyramid Lake’s 

only perennial tributary. Each 

spring, adults migrate to the 

south end of Pyramid Lake and 

await environmental cues to 

migrate into the Truckee River 

to spawn. 
These changes caused the 

Pyramid Lake strain of Lahontan 

cutthroat trout (Oncorhyncus 

clarki) to become extinct by the 

early 1940s. However, the cuiui’s incredible longevity (>50 

years) allowed it to persist until 

high water years enabled it to 

traverse the delta. Even at that, 

spawning was infrequent enough 

to cause the population to decline. 

In 1967, this trout was listed as an 

endangered species. 

In an attempt to revitalize the 

Pyramid Lake fishery the Marble 

Bluff Fish Passage Facility was 

completed in 1976 to serve as a 

bypass around the Truckee River 

Delta. The facility has been 

improved over the years and is 

now very successful in passing 

cui-ui. More recently, changes in 

Truckee River operations and the 

Truckee-Carson-Pyramid Lake 

Water Rights Settlement Act of

1990 have served to enhance 

Truckee River flows into Pyramid 

Lake. 

For additional information, please 

contact: 

Lyman Thorsteinson, Center Director

U.S. Geological Survey

Western Fisheries Research Center 

6505 NE 65th Street, Seattle, WA 98115

(206-526-6282 FAX (206) 526-6654

http://wfrc.usgs.gov

Cui-ui spawning in the Truckee River

Truckee River 

Lahontan cutthroat trout (Oncorhynchus clarki) 

Whether construction of the Marble Bluff Fish Passage Facility and 

the additional stream flow are sufficient to save the cui-ui has been in 

question. 

 

Biologists from the WFRC developed a cui-ui population viability 

model, which is sensitive to spawning frequency. Scientists are 

currently preparing support papers on cui-ui life history traits and 

survival to be used in the model. The model is intended to insure the 

persistence of cui-ui through wise use of limited water resources that 

are necessary for cui-ui spawning.