Snakehead Fishes and Florida Waters
Walter R. Courtenay, Jr.
U.S. Geological Survey, Center for Aquatic Resources Studies, Gainesville, FL
Two, perhaps three individuals of the northern snakehead, Channa argus, were
released into a 1.8 ha retention pond in Crofton, Anne Arundel County, Maryland,
during 1999 or 2000 by a local resident. This airbreathing species is native from the
Yangtze River basin, China, western Korea, northward to the Amur River along the
Chinese-Siberian border. Up to 90% of its diet consists of fishes. This is the most
prolific snakehead species with large females capable of releasing 155,000 oöcytes
per year in two to 5 spawning events. Maximum size is reported to almost 1.5 m total
length. Temperature tolerance is 0-30º C. This fish was introduced and became
established in Japan (1920s), Czechoslovakia (1956-1960), and Kazakhstan,
Turkmenistan, and Uzbekistan (1961-1964). Attempts to establish the species in
Russia (Moscow Province, 1949-1953) failed.
Presence of this species in the heavily vegetated Maryland pond was discovered in
May 2002 when an angler caught and subsequently released a 41 cm individual after
photographing the fish. Maryland Department of Natural Resources (MDDNR)
personnel sent a digital image of the specimen to the U.S. Geological Survey (USGS)
Center for Aquatic Resources Studies in Gainesville, Florida, in June where it was
identified as a northern snakehead.
On 30 June 2002, another angler caught a 67 cm northern snakehead from the same
pond. A week later, the same angler and his daughter captured several juvenile
snakeheads using dipnets, confirming reproduction. MDDNR biologists subsequently
captured approximately 100 juveniles with electrofishing. The pond in which this
species existed was approximately 68 m from the Little Patuxent River, a pathway,
along with the possibility for transfer to novel waters by anglers, heightened potential
for wider dispersal.
The good news is that, thanks to early tests on captured juveniles by MDDNR and
University of Maryland biologists that proved the northern snakehead susceptible to
eradication by rotenone, the population of snakeheads (over 13,000 fish) was
eliminated from the Crofton pond in early September 2002. A question remains if
this species escaped earlier into the Little Patuxent River. MDDNR, U.S. Fish and
Wildlife Service, and USGS biologists cooperated throughout this endeavor in what
has been termed a “rapid response” effort.
The bad news for Florida is that the same species has been captured from the St.
Johns River near Lake Harney, Seminole and Volusia counties, on two occasions in
2000. Reproduction and establishment have not been verified to date, but are likely.
More bad news is that another snakehead species, Channa marulius, the bullseye
snakehead, was discovered established by Florida Fish and Wildlife Conservation
Commission biologists in 2001 in lakes and canals in Tamarac, Broward County.
This species is reported to reach lengths of 1 meter or more and is a subtropical to
warm temperate species. The really bad news is that neither species is confined to a
body of water from which it could be eradicated. The worst news is that both species
have potential to become established in the Kissimmee drainage and southward. All
snakeheads are predators, mostly feeding on other fishes, with many behaving as
“thrust predators”, darting from rest or hidden locales to engulf prey which, for
several species, can be up to 1/3 the body length of the predator.
Walter R. Courtenay, Jr., Center for Aquatic Resources Studies, U.S. Geological
Survey, 7920 NW 71st Street, Gainesville, FL 32653-3071, Phone 352-378-8181,
x355; Fax: 352-378-4956, walter_courtenay@usgs.gov