U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2004-3074 

July 2004

Invasive Species Program—Snakeheads, 

Aquatic Invaders

Printed on recycled paper

PECTORAL FIN

PELVIC FIN

(almost directly

below pectoral fin)

ANAL FIN

(long)

SNAKEHEAD

BOWFIN

PECTORAL FIN

PELVIC FIN

(in belly region)

ANAL FIN

(short)

What are snakeheads?

Snakeheads are airbreathing freshwater fishes that are not native to North 

America. In scientific terms, snakeheads 

are divided into two distinct genera:

• Channa (snakeheads of Asia, 

Malaysia, and Indonesia); and

• Parachanna (African snakeheads).

In the summer of 2002 and again in 

late spring 2004, one of the Asian species, the northern snakehead, generated 

national media attention when anglers 

caught this fish in a pond in Maryland 

and, more recently, in the Potomac River 

in Maryland and Virginia. Fisheries scientists consider snakeheads to be invasive 

species because they have the potential 

to threaten native fishes, the recreational 

fishing industry, and aquatic ecosystems.

What do they look like?

Snakeheads have a long, cylindrical body with a large mouth and sharp 

teeth. They have enlarged scales on top 

of their heads and their eyes are located 

far forward on their head, similar to 

the scale patterns and eye positions of 

snakes. Because their heads 

are similar to the heads of 

snakes, they have long been 

known by the common name 

“snakeheads.” Size and 

color patterns vary among 

29 recognized species. The 

largest recorded snakehead 

was almost 6 feet in length. 

Additionally, the young 

(juveniles) of many species 

often have color patterns dramatically 

different from the coloration of adults. 

Adult snakeheads superficially resemble 

the bowfin, a native North American fish. 

Where are they from?

Snakeheads are native to parts of Asia 

and Africa. Fishery scientists have found 

individuals of four species in waters 

of California, Florida, Hawaii, Maine, 

Maryland, Massachusetts, Rhode Island, 

Virginia, and Wisconsin. Reproducing populations, however, have been 

documented only in Florida, Hawaii, 

and Maryland. The blotched snakehead 

(Channa maculata) has thrived in Oahu, 

Hawaii, for more than a century; the 

bullseye snakehead (C. marulius) was 

discovered thriving in Florida in 2000. 

An isolated reproducing population of 

northern snakeheads was eradicated in 

Maryland in 2002. Captures of northern snakeheads of several different 

sizes in the Potomac River, Maryland 

and Virginia, in late spring and during 

summer 2004 indicates that this species is 

likely reproducing there.

How did they get here?

Prior to being added to the list of 

injurious wildlife under the Lacey Act in 

October 2002, which banned import and 

interstate transport without a permit from 

the U.S. Fish and Wildlife Service, snakeheads were sold in pet stores and in live 

food fish markets and some restaurants 

in several major U.S. cities, including 

Boston, New York, and St. Louis. Live 

specimens have been confiscated by 

authorities in Alabama, California, 

Florida, Texas, Virginia, and Washington where possession of live snakeheads 

is illegal. Some snakeheads living in 

Northern snakehead (Channa argus) Illustration by Susan Trammell
natural waters of the U.S. may have been 

released by aquarium hobbyists or those 

hoping to establish a local food resource. 

Also, some cultures practice “prayer 

animal release,” a faith-based activity in 

which individuals purchase, then release, 

an animal (fish, amphibian, reptile, or 

bird) to earn merits with a deity.

What are the potential effects to 

our waters?

During all life stages, snakeheads 

compete with native species for food and 

habitat. As juveniles, they eat zooplankton, insect larvae, small crustaceans, and 

the young of other fishes. As adults, they 

become voracious predators, feeding on 

other fishes, crustaceans, frogs, small 

reptiles, and sometimes birds and small 

mammals. Should snakeheads become 

established in North American ecosystems, their predatory behavior could drastically disrupt food webs and ecological 

conditions, thus forever changing native 

aquatic systems by modifying the array 

of native species.

An additional concern is the snakehead’s potential to transfer pathogens to 

native fishes, because snakeheads can 

carry diseases and parasites that have the 

potential to be harmful. Fishery scientists 

need to study this potential to determine 

if diseases and parasites can be transferred to North American species.

Have snakeheads been 

introduced to places other than 

the United States?

Northern snakeheads were purposefully introduced and established into 

Japan in the early 1900s. They were 

introduced into parts of the former Soviet 

Union (Kazakhstan, Uzbekistan, Turkmenistan) when accidentally mixed with 

shipments of imported Asian carps. This 

fish also became established in Russia 

for a short time in the 1950s and was 

successfully introduced into Czechoslovakia. The blotched snakehead was successfully introduced into the Philippines 

and into Madagascar where it is now 

a major threat to many of the endemic 

cichlid fishes of that island nation. 

The chevron snakehead (Channa striata)

was successfully introduced into the 

Philippines, is reported to be established 

in other Pacific islands, and is being 

cultured in Hawaii.

Do snakeheads “walk?”

Although claims of their mobility have 

been greatly exaggerated, several species 

of snakeheads are able to wriggle overland from one body of water to another, 

particularly if the ground is wet. They do 

this by flexing their body and pushing 

with their tail, while using their broad 

pectoral fins to stabilize their head. It is 

unknown how far they can travel on land. 

This crawling ability is reduced in larger 

species of snakeheads as they reach adulthood. The introduced blotched snakehead in Madagascar is known to crawl 

onshore, allow its body to be covered 

with ants, then return to the water where 

the ants are dislodged and subsequently 

eaten by the fish.

How many eggs do snakeheads lay?

A mature northern snakehead female 

can carry as many as 50,000 eggs, 

although some will not develop and 

others will be eaten by insects and small 

fishes following fertilization. Depending 

on water temperature, eggs can hatch in 

about 24-48 hours. When the fry hatch, 

they remain clustered at the surface of the 

nest until their fins develop. At that time, 

the young (early juveniles) begin swimming by diving down into the center of 

the nest, then rising back to the surface. 

Early juveniles remain in the nest for 

3-4 weeks, schooling, and being guarded 

by one or both parents. All species of 

snakeheads guard their eggs and young, a 

behavior that is rare in our native fishes.

Juvenile snakeheads (fry) cluster at the 

surface of their “nest,” a column of water 

cleared from vegetation in 2-3 feet of water. 

Their parents will aggressively guard their 

nest for 3-4 weeks while the fry develop their 

fins, learn to school, and are ready to fend for 

themselves.
The reproductive behavior of snakeheads is quite interesting. Most, perhaps 

all, are nest builders. The northern 

snakehead, for example, builds its nest 

in shallow water by clearing an area of 

vegetation. This results in a cylindrical 

column of water devoid of most vegetation. Nests are about 2-3 feet deep and 

about 3 feet in diameter. 

A few species of snakeheads are 

mouthbrooders; that is, one of the 

parents will carry fertilized eggs in its 

mouth cavity. When the fry hatch, they 

are retained in the mouth until their fins 

develop to the point the young can swim. 

Even after the young leave the mouth of 

the adult, the parents continue to guard 

the young fish until they are able to fend 

for themselves.

What eats snakeheads?

Although little information exists in 

the scientific literature regarding predation on snakeheads, juveniles would be 

the most vulnerable to predation by other 

predatory fishes and some wading birds 

once they leave the nest and their guarding parents. In U.S. waters where snakeheads have become established, the most 

likely predatory fishes on juveniles would 

be gars, larger sunfishes, bass, perch, and 

pike. Because most native fishes could 

not eat the larger species of adult snakeheads, these snakeheads could become 

the top predators within the freshwater 

fish community.

Humans also eat snakeheads. Within 

their native ranges and places where they 

have been introduced, some species are 

considered a delicacy. Several species 

are caught in the wild for food, whereas 

others are cultured.

Where do snakeheads live?

Snakeheads are freshwater fishes 

with little, if any, tolerance for saltwater. 

Within their native and introduced ranges, 

they live in small and large streams, 

canals, rivers, ponds, reservoirs, and 

lakes. Many species can tolerate a wide 

range of pH, and one species living in 

Malaysia and parts of Indonesia prefers 

highly acid waters (pH 2.8-3.8). The 

northern snakehead and several other 

species prefer to live in somewhat dense 

aquatic vegetation where they feed and 

reproduce.

Can snakeheads harm humans?

Most snakeheads will avoid contact 

with humans. However, when guarding 

their eggs or young, they can become 

aggressive if approached. One species, 

the giant snakehead (Channa micropeltes)

native to southeastern Asia, has been 

reported to be aggressive toward humans 

who got too close to their nest. Other 

snakeheads are not as aggressive toward 

humans. 

What is the Federal Government 

doing about snakeheads?

Two agencies within the Department 

of the Interior (DOI) are responsible for 

researching and regulating snakeheads. 

The U.S. Geological Survey (USGS; 

http://www.usgs.gov) is a research arm 

of DOI, and USGS scientists conducted 

extensive, worldwide research on snakeheads that provided a basis for regulating 

their importation and interstate transport 

in the U.S. Funding for that research was 

sponsored through a grant from another 

DOI agency, the U.S. Fish and Wildlife 

Service (FWS; http://www.fws.gov), 

which is responsible for fisheries management, regulations, law enforcement, 

and education. The mission of the FWS is 

to work with others to conserve, protect, 

and enhance fish, wildlife, and plants for 

the continued benefit of the American 

people.

On October 4, 2002, the FWS added 

the snakehead family of fishes (Channidae) to the list of injurious wildlife under 

the Lacey Act. This includes all currently 

recognized species, and any new species 

that may be described within that family 

in the future. By taking this action, snakehead fishes can no longer be imported 

into the U.S. or transported across state 

lines without a permit. Permits for interstate transportation and importation into 

the U.S. can be obtained by calling the 

U.S. Fish and Wildlife Service Division 

• They are very predatory and could alter conditions in our aquatic 

ecosystems.

• They are airbreathers and several species are capable of overland 

migration during some part of their life history.

• They are very aggressive in their efforts to protect their young.

• Some snakehead species have a very large potential range in the U.S.

A recent comprehensive assessment concluded that when these factors 

are combined, snakeheads pose a significant threat to fish and wildlife 

resources of the United States.

What are the major concerns about snakeheads?

• Do not release the fish or throw it up on the bank (it could wriggle 

back into the water). Remember, this fish is an airbreather and can live 

a long time out of water.

• Kill the fish by freezing it or putting it on ice for an extended length 

of time.

• Photograph the fish if you have access to a camera so the species of 

snakehead fish can be positively identified.

• Contact your nearest fish and game agency or the U.S. Fish and Wildlife Service (703-358-2148) as soon as possible. Keeping data on the 

size, number, and location of where snakeheads are caught or seen is 

vital to controlling this invasive fish.

What should be done with a captured snakehead?
of Management Authority at 1-800-358-

2104. Such permits, however, will only 

be issued for specific uses, such as medical or scientific research and education.

This injurious wildlife listing is based 

upon a thorough review of the scientific data on snakehead fishes and a risk 

assessment that was prepared for the 

FWS by the USGS. The FWS determined 

that regulation of all snakehead species 

is necessary to protect wildlife from the 

purposeful or accidental introduction of 

snakeheads into the ecosystems of the 

United States.

Can aquarium hobbyists still 

possess snakeheads as pets?

As mentioned previously, importation 

of live snakeheads and their interstate 

transport is prohibited. Many states 

prohibit possession of snakeheads, and 

several of those states have done so for 

decades. Aquarists can obtain information about regulations concerning 

possession of live snakeheads and other 

prohibited fishes by contacting their state 

fish and game agency. Transporting live 

snakeheads across a state line for any 

purpose, however, is a Federal offense 

under the Lacey Act, even between two 

states that allow possession of live snakeheads.

Can snakeheads still be 

purchased for food purposes?

Dead snakeheads––on ice or 

frozen––can be imported for food 

purposes to any state except those where 

importation or possession of dead snakeheads is illegal. Live snakeheads of one 

species being cultured in Hawaii, but not 

exported to the mainland of the U.S., 

are available in one market in Honolulu. 

Hawaii regulations require that all fish 

must be killed and their gills removed 

before the purchaser leaves the store. 

An invasive species is an 

introduced, nonnative organism (disease, parasite, plant, or 

animal) that begins to spread 

or expand its range from the 

site of its original introduction 

and has the potential to cause 

harm to the environment, the 

economy, or to human health. 

A few well-known examples 

include the unintentional 

introduction of the West Nile 

virus, chestnut blight, the South 

American fireant in the southeastern states, zebra mussels, 

and lamprey eels in the Great 

Lakes, in addition to the intentional introductions of salt 

cedar (Tamarisk) in the southwest, kudzu vine in the southeast, house sparrows, starlings, 

and nutria in Louisiana and 

Maryland. 

Although the U.S. depends 

on many intentionally introduced nonnative plants and 

animals for our food supply, 

most are “domesticated” to 

be noninvasive (the introduction of potatoes and cattle, for 

example). In the past century, 

however, an increasing number 

of exotic plants and animals 

have been brought to the U.S. 

for other reasons. Many invasives have been unintentionally 

introduced as “hitchhikers” 

with imported species of plants, 

some animals have escaped 

or have been purposefully 

released, and many are now 

environmental and economic 

threats. A study conducted at 

Cornell University estimated 

the annual environmental and 

economic costs due to invasive 

species of plants and animals at 

$137 billion.*

*Source: Pimentel, D., Lach, L., Zuninga, R., 

and Morrison, D., 2000, Environmental and 

economic costs of nonindigenous species in the 

United States: Bioscience: v. 50, p. 53-65. 

What is an invasive species and why should the 

American public be concerned?

For More Information, 

Contact:

U.S. Fish and Wildlife Service

Division of Environmental Quality

Branch of Invasive Species

4401 N. Fairfax Drive, 

Suite 840

Arlington, VA 22203

(703) 358-2148

http://contaminants.fws.gov/

Issues/InvasiveSpecies.cfm

U.S. Geological Survey

Florida Integrated Science Center

Center for Aquatic Resources

 Studies (CARS)

7920 N.W. 71st Street

Gainesville, FL 32653

(352) 378-8181

U.S. Fish and Wildlife Service

(800) 344-WILD (800-344-9453)

http://www.fws.gov

The following report provides 

additional information on snakeheads and is available in HTML 

and downloadable pdf:

Courtenay, W.R., Jr., and 

Williams, J.D. 2004. Snakeheads (Pisces, Channidae)––

A Biological Synopsis and Risk 

Assessment: USGS Circular 

1251, 143 p. 

http://cars.er.usgs.gov/

(warning–this pdf is 53 megabytes)

An informative and continually 

updated website database on 

nonindigenous plants and animals 

in the U.S. can be found at: 

http://cars.er.usgs.gov.

and a site that provides information on invasive species is:

http://www.protectyourwaters.net