Colorado River water is used by more than 22 

million people in the USA and Mexico. Large 

reservoirs store spring runoff which historically 

flowed to the sea. Remaining portions of the river 

were straightened and deepened to more effectively deliver water to downstream 

users. As a result, the river 

no longer physically, nor 

biologically, resembles the 

river of a century ago.

Native fish do spawn but 

their young are eaten by 

introduced predators like 

channel catfish, largemouth 

bass, bluegill, striped bass, 

crappie. Nearly 45 species 

have been successfully introduced. Self-sustaining populations of natives are simply 

gone and their continued

existence in the river is 

dependent upon stocking. 

Native fish do prosper 

when stocked in ponds by 

themselves. Here they form 

semi-natural communities 

where young survive and 

complete their live cycle. 

Cibola and Imperial 

National Wildlife Refuges 

contain two such 

sanctuaries: the Desert 

Pupfish Pond found near 

the Visitor Center and Big-River 

fish sanctuaries located adjacent 

to the river.

Razorback 

suckers feeding near the 

surface at 

High Levee 

Pond.

USGS and 

FWS biologists studying 

the fish at 

High Levee 

Pond.

Native Fish 

Sanctuaries 

of the Lower 

Colorado River

Historically, the Colorado River was one of the 

most formidable rivers in the world. Each spring, 

melting snow from the mountains scoured the desert 

landscape moving millions of tons of sediment to 

the sea. The Grand Canyon lays testament to its 

erosive nature. Summer heat would bring seasonal 

droughts, reducing the river to a trickle impacting 

humans, animals, and fish. 

Laguna Dam during the flood of 1922. 

Isolated by high mountains and harsh deserts, its 

fish community developed unique and specialized 

traits that helped them survive raging floods and 

prolonged droughts. Conditions were so unique that 

three quarters of the fish species are found nowhere 

else in the world. 

The lower river contained nine freshwater fish species, but today, only three freshwater forms remain. 

Others have long disappeared due to introduced 

gamefish and water development that changed the 

landscape. Of the original nine fishes, seven are 

federally listed as endangered, including the three 

described here. The remaining two have retreated 

further upstream and are species of concern. 

A natural 

colored (top) 

and unusual 

“golden” 

bonytail found 

in High levee 

pond.

Young bony- tail love to 

hide in the 

entrance of 

beaver dens 

where they are 

safe from bird 

predators.

“The River” in 1938

“The Canal” in 2000 (same 

location as above)

U.S. Department of the Interior

U.S. Geological Survey

Native Fish 

Sanctuaries 

of the Lower 

Colorado River

For more information on the native fish and history of the lower 

Colorado River, the U.S. Geological Survey, and the U.S. Fish 

and Wildlife Service, visit the following internet sites: 

www.fort.usgs.gov/products/publications/10026/10026.asp. 

www.usgs.gov 

www.fws.gov

Cibola High Levee Pond

Desert Pupfish Pond

General Information Product 9
• Desert pupfish are small, typically measuring less 

than 2.5 inches. Mature males are typically larger 

than females and become quite colorful during 

breeding season. Their bodies turn a beautiful 

bright blue with bright yellow tails. Females are 

small and have dark brown or olive bars.

• Pupfish can tolerate salinities more than twice that 

of seawater. They thrive in habitats where few 

other fish can survive. They occur in desert springs 

and shallow, sandy margins of small streams where 

they feed on a wide variety of small invertebrates 

and algae.

• They are short-lived, seldom living more than a 

year. Fish reach sexual maturity within 6 weeks. 

Males are territorial, aggressively protecting an 

area of about a square yard. Spawning occurs 

between April and October. Females lay up to 800 

eggs which hatch in about 10 days. Larval fish 

measure less than a quarter of an inch.

• Where To See--Pupfish can normally be seen 

every day in the refuge next to the Visitor Centers. 

Larger males can be seen aggressively guarding 

their territories. 

Desert Pupfish

Cyprinodon macularius

• The bonytail is a member of the minnow family 

(Cyprinidae) and is only found in the Colorado 

River. It has a streamlined body with an extremely 

thin or “bonytail.” It has small, trout-like scales 

and is darkish-gray in color. Large fish develop a 

prominent dorsal hump at the base of the head.

• A great deal of its early life ecology was learned 

at High Levee Pond. The fish spawn along the 

shore where gravels have been disturbed by beaver. 

Spawning occurs in early April and usually results 

in thousands of young.

• The bonytail is long-lived (30+ years) as is the 

razorback sucker. Three bonytail taken from Lake 

Mohave were estimated to be 34 to 49 years old. 

Scientists speculate that longevity was an adaptation 

for an extremely harsh environment when conditions

did not always allow for annual spawning. 

• Where To See--The bonytail is the most secretive 

of the three, hiding in aquatic vegetation, underwater brush and in larger rip-rap (rock). Young fish 

can be detected on calm days after sunset. They 

cause a rippling effect on the surface as they feed 

on emerging insects and zooplankton.

Bonytail Chub

Gila elegans

Razorback Sucker

Xrauchen texanus

• Razorback sucker is only found in the Colorado 

River and is the largest of several suckers found in 

the basin. It reaches weights up to 18 pounds and 

lengths of over 2 feet. Its body is elongated and 

adults have a unique dorsal keel protruding from 

behind their head. The keel’s purpose is unknown, 

but theories include its use to stabilize the fish in 

swift water and as a structure to prevent adults 

from being eaten by large predators. It has a large 

sucker-like mouth with fleshy lips and papillae 

(small bumps) that helps the fish “feel” for food 

in the muddy waters. They eat plankton and 

small insects. 

• Females become sexually mature their 4th or 5th 

year. A large mature female can lay as many as 

200,000 eggs. Spawning occurs from January 

through March. These fish are also long-lived. 

Unlike the pupfish, females are 10 to 20% larger 

than similar aged males.

• Where To See--During winter months (JanuaryMarch) spawners can be seen spawning along 

shore. These activities often leave sediment 

plumes. They also school along the surface to feed 

on zooplankton during the day. 

• The future of these fish is extremely bleak. Humans 

have devastated the ecosystem where they once 

prospered. The vast expanses of floodplain wetland 

where these fish evolved are nearly gone. It is 

estimated that only 5% of those habitats remain. 

• They were once the most common fishes in the 

region and today they are restricted to a few small 

populations and habitats. The lower Colorado 

River has the dubious distinction of being one of 

the largest rivers in the world with a totally 

replaced fish community. 

• Today, the river and its reservoirs contain no desert 

pupfish, no wild born bonytail, and very few old 

razorback suckers that will die off this decade. 

Bonytail and razorback suckers are being stocked to 

prevent their extirpation but natural recruitment in 

the wild continues to be prevented by 

non-native predators.

• Societies’ dependence upon water makes native 

fish recovery economically and politically unlikely 

and perhaps impossible. Our society has neither 

the technology nor willingness to remove economically important recreational fishes to the extent 

necessary to benefit native communities.

• High Levee Pond represents the only place on earth 

where the bonytail and razorback sucker coexist in 

a natural fish community. Resource management 

agencies are attempting to recreate this community 

but the task is difficult, expensive, and sometimes 

controversial. 

• The continued existence of these fish depends upon 

the support of the concerned public and state and 

federal resource agencies. 

Their Future?

Female

Male