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Aquatic Invasive Species

Aquatic Invasive Species

Several unwelcome aquatic invasive species have made their way into New Jersey waters and many more are knocking at the door. Aquatic invasive plants like Eurasian water milfoil, hydrilla, didymo (rock snot) and water chestnut choke once thriving waterways. Invasive fish species such as the snakehead, flathead catfish, and Asian swamp eel can outcompete other fish, including rarely encountered native species and prized recreational fish, for food and available habitat. Zebra mussels choke intake pipes and cover critical spawning substrate. Many of the same mechanisms which transport invasive plants and animals also transmit diseases such as Viral Hemorrhagic Septicemia (VHS), Infectious Pancreatic Necrosis Virus (IPN) and Largemouth Bass Virus (LMBV) which threaten fish populations.

Why are invasive species a problem?
Invasive species are defined as “a species that is non-native to an ecosystem and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.”

  • Predation: Large snakeheads and flatheads indiscriminately consume any fish species small enough to fit into their enormous mouths.
  • Competition: Food, spawning areas and habitat are sought by invasive fish, leaving less available for desirable species.
  • Habitat Loss: Plants like purple loosestrife or common reed (phragmites) can take over a wetland making it less suitable for native wildlife.
  • Loss of Recreation: Bighead and silver carp threaten recreational boating as these large fish, when startled, leap out of the water high enough to intercept passing boaters.
  • Decreased Property Value: Beautiful lakefront property can be transformed into a weed-choked monoculture once Eurasian water milfoil or water chestnut become established.
  • Economic Impact: Zebra mussels cause millions of dollars of damage each year in the Great Lakes alone.

Potentially Dangerous Fish Species

Northern Snakehead

New Jersey statutes prohibit the possession or release of live, potentially dangerous animals including fish. Dangerous species are defined as “a species that is non-native to an ecosystem and whose introduction causes, or is likely to cause, economic or environmental harm or harm to human health.” The Fish Code identified thirteen such species (see below). These fish are considered to possess the potential for becoming a significant threat to indigenous animals, the environment, or public safety. Possession and/or release of live potentially dangerous fish species is prohibited and if these species are encountered while angling they must be destroyed. All but one of these species, the silver carp, has been found in New Jersey already.

WARMOUTH – Lepomis gulosus

Although common carp are considered an invasive species by most, they are not designated as one of NJ’s ten potentially dangerous fish species, in part because of how widespread they have become. The stocking of common carp is prohibited, in an effort to minimize their establishment into new waters.

Snakeheads, blue catfish, flathead catfish, and Micropterus sp. (not including largemouth and smallmouth bass) are top level predators and may negatively impact the structure of indigenous and established fish populations. Bighead carp and silver carp threaten human health as they leap out of the water when startled and may intercept passing boaters. When unregulated, grass carp are an invasive species that can over-graze aquatic vegetation, thus destroying fish habitat. Green sunfish and warmouths have a larger mouth than the state’s native sunfish, thus have the ability to outcompete native fish. Asian swamp eel, brook stickleback, round goby, and oriental weatherfish are highly tolerant, generalist feeders that compete with native fish.

Oriental Weatherfish
ORIENTAL WEATHERFISH – Misgurnus anguillicaudatus

Anglers must destroy these species if encountered while fishing and are asked to submit specimen(s) to Bureau of Freshwater Fisheries personnel for verification. Fish and Wildlife’s fisheries biologists can be reached at 908-236-2118 for northern New Jersey, and at 609-223-6080 for southern New Jersey.

Eel comparison graphic

ASIAN SWAMP EEL – Monopterus albus

American eels are a diadromous native species, using both fresh and marine waters during their lifecycle. These eels are found in nearly every waterbody in New Jersey. American brook lamprey are a harmless native species that serves as an indicator of clean substrate. The Asian swamp eel is an invasive species with documented presence in Silver Lake, a 10-acre waterbody located in Gibbsboro, Camden County.

Invasive Alert – Asian Swamp Eel (pdf, 68kb) by Christopher Smith, Principal Bioloist, 2009 Freshwater Fishing Digest

Catfish comparison graphic

FLATHEAD CATFISH – Pylodictis olivaris

The flathead catfish is considered an invasive species capable of causing ecological damage by out-competing other recreationally important species for food and habitat. Although not a native species, channel catfish are stocked by Fish and Wildlife in select locations as it is a desirable recreational and food species. They do not reproduce in most waters, and in the few where they do, populations do not reach problematic proportions.

Flatheads have been confirmed in the middle section of the Delaware River.

SNAKEHEAD – Channa spp.

Bowfin are native species, actually dating back 250 million years and should be released unharmed. However, snakeheads are invasive and should be destroyed and submitted to Fish and Wildlife for verification.

Snakeheads were first found in the lower Delaware River and its tributaries in 2008. The species is now widely distributed throughout the Delaware River basin.


New Jersey lists three carp species as Potentially Dangerous Fish Species:

Grass Carp

GRASS CARP (DIPLOID)  Ctenopharyngodon idella

Silver Carp

SILVER CARP  Hypophthalmichthys molitrix
(Not yet documented in NJ waters)

Bighead Carp

BIGHEAD CARP   Hypophthalmichthys nobolis


The introduction of invasive aquatic plants not only affects the waterbody ecology but negatively affects the local economy of a lake community. Before leaving any body of water all aquatic plants should be removed from boats, motors and trailers.

Water Chestnut Management Activities: 2010 (pdf, 8kb)


How to Identify Zebra Mussels

  • Look like small clams with a yellowish or brownish “D”-shaped shell, usually with alternating dark and light colored stripes.
  • Up to two inches long, but mostare under an inch.
  • Usually grow in clusters
  • Zebra mussels are the ONLY freshwater mollusk that can firmly attach itself to solid objects-rocks, dock pilings, boat hulls, water intake pipes, etc.

What to Do If You Find a Zebra Mussel

  • Note the date and precise location where the mussel or its shell was found.
  • Take the mussel (several if possible) with you and store in rubbing alcohol. Do not throw it back in the water.
  • Immediately call Dr. Peter Rowe, New Jersey Sea Grant Headquarters, 732-872-1300 extension 31, or write
ORIENTAL WEATHERFISH - Misgurnus anguillicaudatus

Be a Responsible Angler

Angler and boater cooperation is critical to minimize the spread of aquatic invasive species and disease. Follow these guidelines for every fishing trip:

  • Never, ever move fish from one waterbody to another. Relocating fish transfers disease and parasites between waterbodies. The practice also undermines Fish and Wildlife’s stocking and management programs, wasting valuable time and money. Fish from an aquarium also must never be released into a local pond, lake or stream.
  • Handle fish as gently as possible if they are to be released. Less stress equates to better disease resistance.
  • Refrain from hauling fish for long period in livewells if fish are to be released.
  • If interested in stocking fish, a Fish Stocking Permit is required in most instances; see the Freshwater Fisheries Permits page for information and application form.
  • Do not release live bait into any body of water.
  • Stage weigh-in tournaments during cooler weather so fish caught will be stressed less. Utilize “paper” tournaments during hot weather, with anglers measuring and immediately releasing the fish.
  • Switch to wearing rubber-soled boots instead of felt.
  • Drain your livewell, bilge and bait tanks before leaving the body of water where you’ve been boating or fishing.
  • Remove all mud, aquatic plants and animals from all gear, boats, motors and trailers before leaving the body of water where you’ve been boating or fishing.
  • Thoroughly clean and dry livewells, boats, trailers and other equipment between fishing trips. A light bleach solution is an excellent disinfectant for cleaning equipment (1 cup bleach for 10 gallons of water). For livewells, use ¼ cup bleach per gallon of water. The contact time with bleach should be at least five minutes. (In a waterbody known to contain VHS, clean and disinfect livewells and bait wells with a 10 percent chlorine/water solution). Rinse well to remove all residual chlorine.
  • After cleaning, allow boats, trailers and other equipment to dry fully in the sun for four to six hours.
Tournament scene

Tournament Considerations

With the increasing popularity of tournament angling and growing potential for spreading invasive species and diseases, organizers are encouraged to follow proper procedures for disinfecting boats, trailers and equipment after each fishing trip. Popular fishing destinations such as Lake Champlain, the Hudson River and Oneida Lake are infested with zebra mussels and water chestnut. Hydrilla is found in the Potomac River and Susquehanna Flats. Eurasian milfoil is found in many waters throughout the northeast and mid-Atlantic region.

Taking proper precautions like disinfecting equipment and educating fellow anglers will ensure the protection of New Jersey’s waterbodies from these invaders.


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Copyright © State of New Jersey, 1996-2023
Department of Environmental Protection
P. O. Box 420
Trenton, NJ 08625
Last Update: August 9th, 2023