Fish similar in appearance

The eyespot bowfin (Amia ocellicauda) and northern snakehead can be found in the same waters on the swampy tidal coastal plain of the mid-Atlantic United States, such as the Potomac and Delaware River, and are commonly confused with each other. Some contrasting differences in northern snakehead include the lack of a black eyespot on their caudal peduncle, a golden tan to brown coloration with dark splotches, a longer anal fin, a more elongated head, and an upper jaw that is shorter than its lower jaw. Another noticeable difference is that northern snakehead scales continue uniformly from their body to their head. The northern snakehead has scales that continue uniformly from the body through to their head, whereas bowfin heads are smooth and free of scales.^[8]

Japan

Snakeheads of Korean stock were first introduced to Japan in the 1920s, and since then have spread to about every suitable body of water on the Japanese mainland.^[14]

Europe

During the Cold War, the USSR imported several different species of fish from eastern Eurasia into Europe for new prospects in aquaculture. Among these fish was the northern snakehead, which came from the Amur River basin and were stocked in various ponds of the Moscow region starting in 1949.^[15] These initial experiments were successful and it was recommended that snakehead be stocked into various other waterbodies. However, only one shipment to Czechoslovakia was ever made in 1955, and nothing else after. The snakehead was also introduced to the Volga Delta and various ponds in Yekaterinburg, but are presumed to have failed due to no reports since then.

While the snakeheads were reported to have been breeding in Moscow in the 1950s, they have since disappeared. There are no known populations in Europe in this moment.

Central Asia

The snakehead has managed to establish themselves in the countries of Kazakhstan, Turkmenistan, and Uzbekistan, all of which used to be part of the former Soviet Union. More specifically, they are known to be in the Amu Darya, Syr Darya, and Kashka-Darya since the 1960s due to both accidental and intentional releases. Since then, snakeheads have also been introduced to the Sarysu River, Talas River, and Chu River. They have become an important commercial fish in the region, with around 10 metric tons being harvested from just the Talas in 1989.

United States

The fish first appeared in U.S. news when an alert fisherman discovered one in a Crofton, Maryland, pond in the summer of 2002.^[16] 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 adults and over 100 juvenile fish were found and destroyed. A man admitted having released two adults, which he had purchased from a New York market, into the pond.^[17]

Northern snakehead in shallow water

In 2004, 19 northern snakeheads were captured in the Potomac River, and they were later confirmed to have become established (i.e., they were breeding). They are somewhat limited to that stretch of the river and its local tributaries, upstream by the Great Falls, and downstream by the salinity of Chesapeake Bay.^[17] Tests found they are not related to northern snakeheads found in other waters in the region, alleviating some concern of their overland migration.^[18] Northern snakeheads continue to be caught in the river as of 2022.^[19][20]

The northern snakehead has been found in three counties of Florida, and may already be established there. Apparently unestablished specimens have been found in Flushing Meadows–Corona Park, New York City, two ponds in Philadelphia,^[17] a pond in Massachusetts, and reservoirs in California and North Carolina.^[2] In 2008, the northern snakehead was found in drainage ditches in Arkansas as a result of a commercial fish-farming accident. Recent flooding may have allowed the species to spread into the nearby White River, which would allow an eventual population of the fish in the Arkansas and Mississippi Rivers.

In the summer of 2008, an infestation of the northern snakehead was confirmed in Ridgebury Lake and Catlin Creek near Ridgebury, New York. By August 2008, the New York State Department of Environmental Conservation had collected a number of the native fish, and then poisoned the waters with a liquid rotenone formulation. After the poisoning, the NYSDEC had to identify, measure, and additionally process the fish to adhere with Bureau of Fisheries procedures before disposal. The treatment plan was operated under several agents, and New York State Police were placed on stand-by in case of protests of local residents of the area.

A new concern is that this fish's spreading is getting close to the Great Lakes, which it may enter and disrupt that ecosystem.

When the snakehead was found in Crofton, the piscicide rotenone was added to the three adjacent ponds.^[2] This method of containment killed all fish present in the water body to prevent the spread of the highly invasive snakehead. The chemical breaks down rapidly, and has a half-life in water of 1–3 days.^[21][22]

In 2012, a snakehead was found in a pond in Burnaby, British Columbia, but further study revealed that it had been released three months or less before its capture and it was a blotched snakehead or perhaps a hybrid involving that species.^[23] Unlike the northern snakehead, which potentially can establish a population in parts of Canada, the blotched snakehead generally only lives in warmer waters.^[23] Before its exact identity was revealed, the province introduced legislation banning the possession of snakeheads and several other potentially invasive species.^[23]

In April 2013, sightings of the species in Central Park's Harlem Meer prompted New York City officials to urge anglers to report and capture any individuals. Ron P. Swegman, author of several angling essays on Central Park's ponds, confirmed the species had put both anglers and the New York State DEP on high alert.^[24][25]

In late 2013, authorities in Virginia and Maryland were counting snakeheads in the Chesapeake Bay to better understand the impact of the introduction of the fish to the local ecosystem.^[26] Virginia has criminalized the "introduc[tion]" of snakeheads into the state without specific authorization, although the relevant statute does not explain whether mere importation is sufficient to constitute "introduc[tion] into the Commonwealth" or whether instead release into the environment is required.^[27]

In October 2019, multiple snakeheads were found in a pond on private property in Georgia.^[28][29][30]

In August 2021, a 30-inch snakehead weighing 5 pounds was caught in a reservoir in Canton, Massachusetts.^[31]