Giant Snakehead Fish - US Invasive Species

Are snakehead fish a dangerous invasive species in the USA? Invasive species, whether they are animals, fish or plants, are causing a huge problem around the world. An invasive species can cause huge disruptions to fragile, local ecosystems, as they often have no natural predators in their new habitat, take over territory and food sources required by indigenous animals for survival and sometimes even destroy terrain. The discovery of a new invasive species in an area for the first time is always a cause for concern. However, sometimes media reactions to such discoveries can throw people into a frenzy and panic by totally overhyping the possible dangers of their presence to the local population and environment. One such invasive species is the snakehead fish in the United States. They have been dubbed ‘Frankenfish’ or ‘fish from hell’ and there are already many urban myths circulating about these introduced fish. It is said that they will voraciously kill and eat everything they come across, that they can survive for up to four days out of the water, that they can travel great distances across dry land to infest new bodies of water, that they have a poisonous bite and that they can be aggressive towards humans and have even killed them.

So what is the truth about snakehead fish? They are fresh water fish and are indigenous to parts of Asia and Africa. There are twenty eight known different types and they can vary tremendously in size and colour. They are apex ambush predators, and feed on other fish species, crustaceans, small amphibians and occasionally birds and small mammals. They can grow to a great size and there have been records of snakeheads being four feet long and weighing more than fifteen pounds. They have long cigar-shaped bodies, large mouths with a protruding lower jaw and sharp teeth and long dorsal and anal fins. Snakeheads start off life ranging in colour from pale greys to golden brown, and darken as they mature to dark browns with black spots. Their preferred habitat is freshwater streams, ponds, ditches and swamps. All snakehead fish are air breathers and they have a high tolerance for water with low oxygen levels. They guard their young and can become very aggressive towards anything that they perceive as a threat to their offspring. They have acquired their name from the enlarged, snake-like scales they have on their heads. Snakeheads sometimes get confused with the native North American bowfin when they are caught by anglers, as they can look fairly similar.

Snakehead fish are considered to be an important food fish in Asia and are imported live into America for the Asian food markets in Boston and New York City. They are also popular aquarium fish and are valued for their aggressive natures and toughness. It is thought that snakeheads that have been found in US waterways have either been pets that have been released by their owners or have been released from live food markets in the hope that a growing local population will become a good food source. The most likely reason that aquarium keepers would have released their snakeheads is that they can no longer afford to feed them, as they are voracious feeders and can consume a great number of prey fish a day. In the summer of 2002 northern snakeheads were caught in Crofton Pond in Maryland, a discovery that caused widespread panic, made the national headlines and local anglers were asked to kill any of these invasive fish that they caught. In October 2002 they were added to the list of injurious species by the US Fish and Wildlife Service, which prevented the transporting of snakeheads between states and banned the importation of all twenty eight species into the USA. It is illegal to possess snakehead fish in thirteen states, but not in Maryland, the District of Columbia or Virginia. It is, however, an offence to release foreign species of fish into Maryland’s waterways. Live snakeheads have been confiscated in many of the States where possession of these fish has been banned, and to exacerbate the problem further, live specimens are readily available to buy on the internet.

Finding individual live snakehead specimens in US waterways is worrying, but the biggest concern is whether or not a breeding population has been established. Breeding populations have been discovered in Maryland, Florida and California, and they have seem to have permanently established themselves in the Potomac River since 2004. In Florida, bullseye snakeheads are breeding in an urban network of canals in the south east of the State. Most worryingly, there have been live specimens of the giant snakehead caught from Maine down to Arkansas. Giant snakeheads are the largest of these predatory fish, and have been known to act aggressively towards humans and even wounded them. A breeding population of giant snakeheads has not yet been found, and hopefully there never will be.

They are voracious apex predators that are potentially capable of decimating the local fish populations, and they also have no natural predators in the US. At all stages of their life they compete with the native fish for food. When they are juveniles they consume zooplankton, small crustaceans, insect larvae and the young of other fish. As adults, 90% of their large appetites are satisfied by eating other fish species, with the remaining 10% consisting of crustaceans, frogs, small reptiles and sometimes even birds and small mammals. They also carry a disease called Epizootic Ulcerative Syndrome, and scientists are desperately working to determine whether or not invasive snakeheads can pass this disease onto indigenous fish. In contained bodies of water, such as ponds, work has been done to eradicate populations of these invasive fish when they are discovered. A chemical called Rotenone has been used to kill the snakeheads, but unfortunately it will also kill any other fish present in the water. It is accepted, however reluctantly, that once a population has established itself in a network of fresh waterways that it is almost impossible to get rid of them. As a female snakehead can produce up to 100,000 young in a year, very large populations of the fish can establish themselves very quickly, potentially causing permanent damaging changes to American aquatic ecosystems.

So while snakeheads are perhaps not the ‘devil fish’ portrayed by a hysterical media, as an invasive aquatic species they have the potential to cause great damage to fragile ecosystems in the US and to out-compete and consume as food the local fish. If you keep them in your aquarium you need to be aware that it is both illegal and totally irresponsible to release them into local ponds or rivers when you wish to be rid of them for some reason. Indeed, we all need to become more aware of the dangers of invasive exotic species in our native ecosystems, and ensure that we do not release any foreign fish, animal or plants into our local areas and also that we report any unusual or exotic species that we do see or catch to the appropriate authorities.

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