Invasive Species Program—Snakeheads, Aquatic Invaders

Invasive Species Program—Snakeheads, Aquatic Invaders 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: Northern snakehead (Channa argus) Illustration by Susan Trammell • Channa (snakeheads of Asia, Malaysia, and Indonesia); and Where are they from? and Virginia, in late spring and during summer 2004 indicates that this species is • Parachanna (African snakeheads). Snakeheads are native to parts of Asia likely reproducing there. In the summer of 2002 and again in and Africa. Fishery scientists have found late spring 2004, one of the Asian spe- individuals of four species in waters How did they get here? cies, the northern snakehead, generated of California, Florida, Hawaii, Maine, national media attention when anglers Maryland, Massachusetts, Rhode Island, Prior to being added to the list of caught this fish in a pond in Maryland Virginia, and Wisconsin. Reproduc- injurious wildlife under the Lacey Act in and, more recently, in the Potomac River ing populations, however, have been October 2002, which banned import and in Maryland and Virginia. Fisheries sci- documented only in Florida, Hawaii, interstate transport without a permit from entists consider snakeheads to be invasive and Maryland. The blotched snakehead the U.S. Fish and Wildlife Service, snake- species because they have the potential (Channa maculata) has thrived in Oahu, heads were sold in pet stores and in live to threaten native fishes, the recreational Hawaii, for more than a century; the food fish markets and some restaurants fishing industry, and aquatic ecosystems. bullseye snakehead (C. marulius) was in several major U.S. cities, including discovered thriving in Florida in 2000. Boston, New York, and St. Louis. Live What do they look like? An isolated reproducing population of specimens have been confiscated by northern snakeheads was eradicated in authorities in Alabama, California, Snakeheads have a long, cylindri- Maryland in 2002. Captures of north- Florida, Texas, Virginia, and Washing- cal body with a large mouth and sharp ern snakeheads of several different ton where possession of live snakeheads teeth. They have enlarged scales on top sizes in the Potomac River, Maryland is illegal. Some snakeheads living in 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 SNAKEHEAD are similar to the heads of snakes, they have long been known by the common name “snakeheads.” Size and PECTORAL FIN color patterns vary among PELVIC FIN ANAL FIN (almost directly (long) 29 recognized species. The below pectoral fin) largest recorded snakehead was almost 6 feet in length. Additionally, the young BOWFIN (juveniles) of many species often have color patterns dramatically different from the coloration of adults. Adult snakeheads superficially resemble PECTORAL FIN PELVIC FIN ANAL FIN the bowfin, a native North American fish. (in belly region) (short) U.S. Department of the Interior Fact Sheet 2004-3074 U.S. Geological Survey Printed on recycled paper July 2004 natural waters of the U.S. may have been for a short time in the 1950s and was hood. The introduced blotched snake- released by aquarium hobbyists or those successfully introduced into Czechoslo- head in Madagascar is known to crawl hoping to establish a local food resource. vakia. The blotched snakehead was suc- onshore, allow its body to be covered Also, some cultures practice “prayer cessfully introduced into the Philippines with ants, then return to the water where animal release,” a faith-based activity in and into Madagascar where it is now the ants are dislodged and subsequently which individuals purchase, then release, a major threat to many of the endemic eaten by the fish. an animal (fish, amphibian, reptile, or cichlid fishes of that island nation. bird) to earn merits with a deity. The chevron snakehead (Channa striata) How many eggs do snakeheads lay? was successfully introduced into the Philippines, is reported to be established A mature northern snakehead female What are the potential effects to in other Pacific islands, and is being can carry as many as 50,000 eggs, our waters? cultured in Hawaii. although some will not develop and others will be eaten by insects and small During all life stages, snakeheads fishes following fertilization. Depending compete with native species for food and Do snakeheads “walk?” on water temperature, eggs can hatch in habitat. As juveniles, they eat zooplank- Although claims of their mobility have about 24-48 hours. When the fry hatch, ton, insect larvae, small crustaceans, and been greatly exaggerated, several species they remain clustered at the surface of the the young of other fishes. As adults, they of snakeheads are able to wriggle over- nest until their fins develop. At that time, become voracious predators, feeding on land from one body of water to another, the young (early juveniles) begin swim- other fishes, crustaceans, frogs, small particularly if the ground is wet. They do ming by diving down into the center of reptiles, and sometimes birds and small this by flexing their body and pushing the nest, then rising back to the surface. mammals. Should snakeheads become with their tail, while using their broad Early juveniles remain in the nest for established in North American ecosys- pectoral fins to stabilize their head. It is 3-4 weeks, schooling, and being guarded tems, their predatory behavior could dras- unknown how far they can travel on land. by one or both parents. All species of tically disrupt food webs and ecological This crawling ability is reduced in larger snakeheads guard their eggs and young, a conditions, thus forever changing native species of snakeheads as they reach adult- behavior that is rare in our native fishes. 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 trans- ferred to North American species. Have snakeheads been introduced to places other than the United States? Northern snakeheads were purpose- fully introduced and established into Japan in the early 1900s. They were introduced into parts of the former Soviet Union (Kazakhstan, Uzbekistan, Turk- menistan) when accidentally mixed with shipments of imported Asian carps. This fish also became established in Russia 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. What are the major concerns about snakeheads? reported to be aggressive toward humans who got too close to their nest. Other snakeheads are not as aggressive toward • They are very predatory and could alter conditions in our aquatic humans. ecosystems. What is the Federal Government • They are airbreathers and several species are capable of overland migration during some part of their life history. doing about snakeheads? Two agencies within the Department • They are very aggressive in their efforts to protect their young. of the Interior (DOI) are responsible for researching and regulating snakeheads. • Some snakehead species have a very large potential range in the U.S. The U.S. Geological Survey (USGS; A recent comprehensive assessment concluded that when these factors http://www.usgs.gov) is a research arm are combined, snakeheads pose a significant threat to fish and wildlife of DOI, and USGS scientists conducted resources of the United States. extensive, worldwide research on snakeheads that provided a basis for regulating their importation and interstate transport The reproductive behavior of snake- Where do snakeheads live? in the U.S. Funding for that research was heads is quite interesting. Most, perhaps sponsored through a grant from another all, are nest builders. The northern Snakeheads are freshwater fishes DOI agency, the U.S. Fish and Wildlife snakehead, for example, builds its nest with little, if any, tolerance for saltwater. Service (FWS; http://www.fws.gov), in shallow water by clearing an area of Within their native and introduced ranges, which is responsible for fisheries man- vegetation. This results in a cylindrical they live in small and large streams, agement, regulations, law enforcement, column of water devoid of most vegeta- canals, rivers, ponds, reservoirs, and and education. The mission of the FWS is tion. Nests are about 2-3 feet deep and lakes. Many species can tolerate a wide to work with others to conserve, protect, about 3 feet in diameter. range of pH, and one species living in and enhance fish, wildlife, and plants for A few species of snakeheads are Malaysia and parts of Indonesia prefers the continued benefit of the American mouthbrooders; that is, one of the highly acid waters (pH 2.8-3.8). The people. parents will carry fertilized eggs in its northern snakehead and several other On October 4, 2002, the FWS added mouth cavity. When the fry hatch, they species prefer to live in somewhat dense the snakehead family of fishes (Channi- are retained in the mouth until their fins aquatic vegetation where they feed and dae) to the list of injurious wildlife under develop to the point the young can swim. reproduce. the Lacey Act. This includes all currently Even after the young leave the mouth of recognized species, and any new species that may be described within that family the adult, the parents continue to guard Can snakeheads harm humans? the young fish until they are able to fend in the future. By taking this action, snake- for themselves.

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