Northern snakeheads arrived in the United States primarily through the live food fish market. Importers brought them in from Asia to supply ethnic markets and restaurants, and the fish were then released, either intentionally or accidentally, into local waterways. Until 2002, importing live snakeheads was perfectly legal, and the northern snakehead made up the greatest volume and weight of all live snakehead species brought into the country.
The Live Food Fish Trade
The northern snakehead is native to China, Russia, and Korea, where it lives in shallow ponds, swamps, canals, and slow-moving rivers. It’s a popular food fish across East and Southeast Asia, prized for its firm white flesh. That demand followed immigrant communities to the United States, and by the 1990s, live northern snakeheads were being imported in large quantities to stock tanks at fish markets in major cities.
Historical import records show shipments coming from a surprisingly wide range of countries, including China, Korea, Thailand, Indonesia, and even Nigeria. The fish were sold live because freshness is valued in many traditional cuisines, and keeping them alive in tanks until purchase was standard practice. This created a pipeline of living, breathing predatory fish sitting in shops and warehouses across the country, just one careless moment away from reaching open water.
How They Ended Up in the Wild
The most well-documented case happened in Crofton, Maryland, where a man reportedly bought live northern snakeheads at a market, kept them for a time, and then released them into a local pond. That population was discovered in 2002 and made national headlines. But Crofton wasn’t an isolated incident. The U.S. Geological Survey and the Fish and Wildlife Service have identified unauthorized intentional release from aquariums and live food markets as the primary mechanism for introduction, and it likely happened in multiple locations over several years.
Some releases were practical: a fish market owner disposing of unsold stock, or a home aquarium keeper who underestimated how large and aggressive the fish would become. Northern snakeheads can grow to over three feet long and will eat nearly anything that fits in their mouths, making them poor long-term pets. Others may have been motivated by cultural practices. Some traditions involve “prayer animal release,” a faith-based activity where a person purchases a live animal and sets it free to earn spiritual merit. The USGS has noted this as a contributing factor in snakehead introductions.
Why They Survived So Easily
Most released aquarium fish die quickly in unfamiliar environments. Northern snakeheads are built differently. They have a specialized organ near their gills that functions somewhat like a primitive lung, allowing them to breathe atmospheric air. This makes them obligate air-breathers, meaning they actually need to gulp air at the surface to survive, even in well-oxygenated water.
This adaptation lets them thrive in stagnant, oxygen-poor water where other predatory fish would suffocate. They tolerate water temperatures from freezing to above 86°F (30°C), can survive extended periods under ice by slowing their metabolism, and handle brackish water with salt concentrations up to about 15 to 18 parts per thousand. They can even survive out of water for short periods if their skin stays moist. In short, almost any pond, marsh, or slow creek in the eastern United States is a viable home for them.
The Federal Ban That Came Too Late
The Crofton discovery triggered a swift regulatory response. In October 2002, the U.S. Fish and Wildlife Service added all snakehead species in the family Channidae to the federal list of injurious wildlife under the Lacey Act. This made it illegal to import live snakeheads into the United States or transport them across state lines without a special permit for scientific, educational, or zoological purposes. No live snakehead, its offspring, or viable eggs can be sold, donated, or transferred to anyone without federal authorization.
But the ban addressed the front door after the fish had already slipped in through the back. By 2002, reproducing populations were already establishing themselves. The fish were in the Potomac River watershed, and from there they spread through connected waterways across Maryland, Virginia, and beyond. Today, northern snakeheads have been documented in more than a dozen states.
What They’ve Done to Native Fish
The ecological damage has been significant and well-measured. A study in the Chesapeake Bay watershed compared fish communities in estuarine marshes before and after snakeheads established themselves. Of the 22 species found in both survey periods, 19 declined in relative abundance. The hardest-hit species included white perch, bluegill, black crappie, brown bullhead, and pumpkinseed. Several species disappeared entirely from survey areas, including banded killifish, striped killifish, largemouth bass, and redfin pickerel.
In the Blackwater River system, average species richness dropped from about 27 species to 21 after snakeheads moved in. Perhaps more telling, species dominance, a measure of how unevenly the fish community is distributed, jumped from 0.38 to 0.60. That means the ecosystem shifted from a relatively balanced community of many species to one dominated by a few. Northern snakeheads and blue catfish (another invasive species) increased in abundance while popular prey fish declined. The pattern held across multiple rivers and seasons.
Current Rules for Anglers
State wildlife agencies now actively encourage people to catch and kill northern snakeheads. In Maryland, anglers need a valid fishing license but face no seasons, size limits, or catch limits for snakeheads. If you catch one and intend to keep it, you must kill it immediately. Possessing or transporting a live northern snakehead is illegal under both state and federal law. If you don’t want to keep the fish, you can release it, but only immediately and directly back into the same water where you caught it. You cannot move a live snakehead to any other body of water under any circumstances.
Other states with established snakehead populations have similar policies. The goal is straightforward: remove as many as possible from the wild while preventing any new introductions. Given how well the species tolerates diverse environments and how quickly it reproduces, complete eradication is unlikely in waterways where it’s already established. Management now focuses on controlling the population and protecting native species in areas the snakehead hasn’t yet reached.