Reeling in Frankenfish

It grows to almost three feet long, prowls streams and lakes up and down the Delaware River, and uses its sharp teeth to gobble up some of the same fish species we put on our dinnerplates. Oh, and it can live out of the water for up to four days provided they are kept moist, and some species can wiggle over small pieces of land into other bodies of water.

Sounds like a Halloween nightmare, but it’s worse. It’s real.

The northern snakehead, Channa argus, also known as “Frankenfish,” is very much alive and thriving in the Delaware River watershed — and in 15 other states. Most recently it was spotted in Georgia for the first time. In all, there are 29 known species of snakeheads.

3 fish shockers
Academy scientists wading in a stream to net fish. The equipment includes a backpack electrofisher which stuns the fish temporarily so they can be studied.

David Keller and the Academy’s Fisheries Section team have been tracking snakeheads in Pennsylvania since 2005, a year after scientists first discovered them in a lagoon in Franklin Delano Roosevelt Park in South Philadelphia, near the sports stadiums. It was the first reported sighting in the Delaware River watershed.

We asked Keller to fill us in on the status of the invasive species in the Philadelphia region 15 years after its discovery here.

Why are northern snakeheads a problem?

They are voracious predators capable of disrupting ecosystems and threatening desirable species wherever they’re introduced. Academy scientists and resource managers are concerned that the species may negatively affect the Delaware River by preying on other fishes and disrupting food webs. They pose a serious threat to endangered species. Because they are an invasive species, the adults have no natural predators where introduced. However, they may be vulnerable to other fishes, particularly when young.

fish w teeth
Sharp teeth are clearly visible on this snakehead.

Is the Frankenfish still in FDR Park’s lagoons and ponds?

Academy scientists have been routinely sampling the FDR Park pond system to track northern snakehead impacts. Data from 2005 to 2008 suggests that the northern snakehead negatively affected other fishes in FDR Park by reducing their numbers, presumably by direct predation and by competition for resources.

How do you know this?

Academy scientists have extensively surveyed the fish assemblage in the FDR park system using electrofishing. We have found sunfishes, American eel, a turtle, and other items in the stomachs of the northern snakehead that we’ve taken from FDR Park. The northern snakehead also has been known to eat white perch, largemouth bass, frogs, crustaceans, small birds, mammals and reptiles.

How about elsewhere?

In the Potomac River, snakeheads feed predominantly on fish, particularly killifishes and sunfishes. In the Delaware River, there is great concern that they may be feeding on, and therefore directly impacting, native and recreational species such as American eel, striped bass, American shad and other popular fishes.

boat and net
A boat the Academy’s Fisheries Section crew uses for electrofishing. Most fish are later released, but not the northern snakehead. David Keller maneuvers the net.

Do northern snakesheads taste good to eat?

Yes, this is one of the reasons why northern snakehead were brought to this country. Live food fish markets would sell northern snakehead prior to it becoming illegal under the Lacey Act in 2002, which banned import and interstate transport without a permit.

What should fishermen and women do if they hook a snakehead?

The best thing people can do is learn to identify the fish and where it is known to occur. If they catch one, they should not release it. They should kill it and report it to the appropriate agency (e.g., Pennsylvania Fish and Boat Commission or New Jersey Fish and Wildlife). It’s illegal to possess live snakeheads in many states.

4 people and fish
Lunchtime in FDR Park, but the northern snakehead held by Academy fisheries scientist Paul Overbeck is not on the menu.

Where did the snakeheads come from?

The northern snakehead is native to eastern China, eastern Russia, and North Korea. In Europe the first report of the species was from Czechoslovakia and Russia in 1949. It was first discovered in Chesapeake Bay watershed two years before it was spotted in the Delaware River watershed.

How did it get into the Delaware River system?

The most likely causes are the exotic pet trade and live food fish markets. People may have had them as pets or purchased them for food and then released them into FDR Park and possibly other portions of the watershed. Northern snakeheads have rapidly expanded their range and now occur in all freshwater tidal portions of the Delaware River and in many non-tidal portions. Recent reports have placed them in the Delaware Water Gap National Recreational Area and near the Upper Delaware Scenic and Recreational River, two areas maintained by the National Park Service and near the start of the Delaware River.

The invasive northern snakehead has been found below the falls of Fairmount Dam at Philadelphia’s iconic Boathouse Row.

Why is the Academy’s tracking data on snakeheads important?

Academy scientists are continuing to study the impacts of this fish, and we are sharing our findings with others so that they can better manage resources where the northern snakehead has been introduced.

If you catch a snakehead in Pennsylvania, contact the Fish and Boat Commission at 610-847-2442 or by email using this contact form.


By Carolyn Belardo and David Keller, fisheries scientist

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