Invasive Species: The Northern Snakehead

What Are Aquatic Invasive Species?

An introduced species is considered "invasive" when the species is non-native to an ecosystem and likely to cause damage to the environment, human health, or the economy. Plants, insects, and many other creatures might be "invasive" depending on where they are. Aquatic invasive species (AIS) like some fish, mollusks, and aquatic plants have the potential to:

• Make water quality worse
• Crowd out native aquatic plants and clog fishing, boating, and swimming areas
• Damage infrastructure like water intake pipes and docks
• Upend the food webs that support native species and popular fisheries
• Introduce new pests and diseases

It has been estimated that the economic cost of invasive species in the United States is upwards of 26 billion dollars per year (Crystal-Ornelas et al, 2021).

How do they get into the environment?

There are several ways AIS can enter the environment. Many AIS were introduced intentionally for sport, aquaculture, or as part of management strategies, often without achieving the intended outcome. In other cases, people released unwanted pets or moved other species around within the United States without considering the widespread impact those species might have in new places. Some AIS were brought into the United States unintentionally. The New Zealand mudsnail (Potamopyrgus antipodarum) and the silty pond mussel (Sinanodonta woodiana), for example, may have hitchhiked into the US in aquaculture shipments. Compared to many plants and animals on land, AIS are less visible, and their presence often goes unnoticed until they are widespread. Rivers, streams, and lakes are highly interconnected, so some species introductions can have especially broad-scale impacts. For example, fingernail-sized zebra and quagga mussels (Dreissena polymorpha & Dreissena bugensis), which hitched a ride in the ballast water of shipping vessels entering the Great Lakes, have spread through the Great Lakes to inland lakes and rivers, including some waterbodies in Pennsylvania, primarily by hitchhiking on boats and fishing gear. Other AIS found in Pennsylvania, like rusty crayfish (Faxonius rusticus), are native to parts of the Midwestern United States but may have been released as live bait elsewhere and now occupy a large range in the eastern United States.

While AIS like zebra mussels and crayfish can have significant negative effects on aquatic ecosystems, invasive predatory fishes can also be very disruptive. Invasive predatory fishes are associated with the decline of native aquatic species worldwide, largely due to their ability to eat a wide variety of prey and out-compete other fish for food and habitat. The northern snakehead (Channa argus)is one example of an invasive predatory fish in Pennsylvania rivers and lakes. The northern snakehead was brought to the United States for sale in pet shops and live-sale fish markets. It is thought that this fish was introduced into the wild following its release or escape from the fish markets. The northern snakehead represents a management challenge because they are sought after for recreational fishing but have negative ecological consequences.

Northern Snakehead (Channa argus)

The northern snakehead (Figure 1) is a large predatory fish that can grow up to three feet in length and is native to Manchuria, China, Korea, and Siberia, where they are a popular source of food. In 2002, northern snakehead were found in a small pond in the Potomac River Basin where they were likely released after purchase from live fish markets. The same year, the northern snakehead were banned for live sale in the United States. After other illicit releases, populations of the fish have dispersed into the Chesapeake Bay watershed, Hudson River, Delaware River Basin (Virginia, West Virginia, Maryland, Delaware, Pennsylvania, and New York), and Arkansas. For more information about their current range, see this map. Although northern snakehead are highly valued in their native range for food, the invasion of these fish in the eastern United States has the potential to reshape local fisheries in ways that are challenging to predict. Northern snakehead populations have expanded quickly after their initial introduction in the United States because they reproduce rapidly. A female northern snakehead can spawn multiple times throughout the warm season and may lay as many as 50,000 eggs in shallow nests of aquatic plants (Rish et al, 2018; Figure 2). Once the larval fish hatch, the adults guard their offspring for several months while the young grow rapidly (Figure 3). 

Northern snakehead prefer shallow ponds, slow-moving streams, and wetland habitats with soft mud and aquatic vegetation. After growing past their larval stages, northern snakehead can survive for long periods out of water by gulping air. This trait allows them to survive in poor water quality, and when they're relatively small, they can move between bodies of water by "crawling" short distances across land. Northern snakeheads mostly eat other fish, but are known to eat whatever organisms they can when fish are scarce. Although it is difficult to predict the impact of this fish as it invades new waters, it has been estimated that even a small population of five or six hundred northern snakehead can consume thousands of pounds of fish per year (Love et al, 2021), which puts pressure on other fish for limited resources. Pennsylvania's fisheries are not only economically important for tourism and food but also play an essential role in the recreation and traditions of many people who live in the Commonwealth.

What Can We Do to Prevent their Spread?

Once an invasive fish like northern snakehead is established in a body of water, complete removal is often not feasible. However, with the help of the public, ecological and economic impacts can be minimized. Angler harvest of invasive fish can help reduce their population size and risk to other fisheries. If you catch a northern snakehead or another invasive species, you should make a report to the Pennsylvania Fish and Boat Commission or call the Commission at 814-359-5163. Anglers who encounter northern snakehead are strongly encouraged to harvest the fish, and they’re known to be excellent table fare. It is illegal to transport live northern snakehead so fish should be dispatched where they are caught. Beaching fish around shorelines to kill them is not legal in Pennsylvania or particularly effective for these fish since they may survive and find their way back into the body of water. Northern snakehead are sometimes confused with other native fish species like bowfin and burbot, so proper identification is key before taking action.

Identification

Northern Snakehead 

Northern snakehead (Figure 4) are most easily distinguished by their long dorsal (top) and anal (bottom) fins and their slightly flattened head like that of some snakes. Their dorsal fin has around 50 rays and their anal fin has just over 30. They have multiple bands of small, slender teeth and several larger canine teeth. They are often golden-brown in color with dollops of dark brown coloration. The pectoral fin is directly behind the gills and almost aligned with the pelvic fin. Young-of-year northern snakehead can also be confused with other species like the fantail darter (Etheostoma flabellare, Rafinesque, 1819 ), which are sometimes caught while collecting live bait. Fantail and other darter species have a divided dorsal fin and a short anal fin.

Native Look-Alikes

Bowfin (Amia ocellicauda and Amia calva)

Bowfin (Figure 6) are native to much of the Midwest and Eastern United States and can now be found in all the major river drainages in Pennsylvania. Bowfin, like northern snakehead, are also lengthy, cylindrical fish with long, soft dorsal fins and olive-brown coloration. Bowfin can also gulp air, prefer slow-moving freshwater and marshes, and have tolerance for brackish coastal plains. Because of these preferences, their habitat may overlap with northern snakehead. While they have a long dorsal fin, they have a much shorter anal fin than the northern snakehead and often have a lower jaw which is shorter than their upper jaw. Bowfin have pelvic fins that are further down their body and have a more rounded head. Some bowfin also have an "eyespot" on their tails.

Burbot (Lota lota)

Burbot (Figure 7) are a tan bottom-dwelling predatory fish that can also look like northern snakehead. In PA, they are an uncommon species that occupy colder bodies of water like Lake Erie and the start of the Allegheny River in northwest Pennsylvania. In the Allegheny River, burbot are state-listed as endangered and are closed to harvest, but they may be caught and eaten in Lake Erie. Currently, burbot tend not to share habitat with northern snakehead because of their colder water preferences. They have a divided dorsal fin that runs about half of the length of their body and a long anal fin that is around the same length as the dorsal fin. Burbot have a single whisker-like barbel on the bottom of their chin and lack the sharp canine teeth of northern snakehead. Northern snakehead do not have a barbel.

• Visit this online map to see a current range map of northern snakehead. 
• Visit this webpage for more information on what you can do about invasive species. 

Citations: 

Crystal-Ornelas R. Hudgins E.J. Cuthbert R.N. Haubrock P.J. Fantle-Lepczyk J. Angulo E. Kramer A.M. Ballesteros-Mejia L. Leroy B. Leung B. López-López E. Diagne C. and Courchamp F. 2021. Economic costs of biological invasions within North America. NeoBiota 67: 485–510.

Love, J. W., and J. J. Newhard. 2021. Using published information to predict consumption by Northern Snakehead in Maryland. Transactions of the American Fisheries Society 150:425–434. Doi.org/10.1002/tafs.10306

Resh, C.A., M.P. Galaska, and A. R. Mahon. 2018. Genomic analyses of Northern snakehead (Channa argus) populations in North America. PeerJ 6:e4581.