The Northern snakehead (Channa argus) is a fish native to China, Russia, and Korea. In the United States, the fish is considered to be a highly invasive species.
The distinguishing features of the northern snakehead are a long dorsal fin, small head, large mouth, big teeth, length up to 40 in (1.0 m), and weight up to 15 lb (7 kg).
The northern snakehead is a freshwater species and cannot tolerate salinity in excess of ten parts per thousand (Courtenay and Williams 2004). The fish’s unusual respiratory system allows it to live outside of water for several days, where concern is that it might wriggle its way to other bodies of water or be transported by humans. Only the young of this species (not adults) may be able to move overland for short distances using wriggling motions (Courtenay and Williams 2004). The preferred habitats of this species are stagnant water with mud substrate and aquatic vegetation, or slow muddy streams; it is primarily piscivorous but is known to eat crustaceans, other invertebrates, and amphibians (Okada 1960). The northern snakehead is capable of spawning more than once in a breeding season (Courtenay and Williams 2004). They build spawning nests in aquatic vegetation and females discharge eggs over the nest, which are externally fertilized by males (Okada 1960).
In many areas of the world, the snakehead fish is considered to be an important food fish. Due to its economic value, Channa argus has been introduced (intentionally or not) to several areas in the continental United States. In the U.S., the snakehead is a top-level predator. Introduction of Channa argus poses a substantial threat to native fish populations.
The fish first appeared in U.S. news when an alert fisherman discovered one in a Crofton, Maryland, pond in the summer of 2002. The snakehead fish was considered to be a threat to the Chesapeake Bay watershed, and wary officials took action by draining the pond in an attempt to destroy the species. The action was successful and two adult and over 100 small fish were found and destroyed. In 2004, many northern snakehead were captured in the Potomac River, and officials expressed concern that a wild population might have been established. This was confirmed in 2005. Northern snakehead individuals continue to be caught on both the Maryland and Virginia sides of the Potomac River. Snakeheads (northern and other species) have been found in Florida, Illinois, North Carolina, California, Pennsylvania, Massachusetts, and Tennessee.
When the snakehead was found in Crofton, the pesticide Rotenone was added to the water. This method of containment killed all fish present in the water body to prevent the spread of the highly invasive snakehead.