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, firstname.lastname@example.org