10 of the Most Invasive Fish Species in the World

A red lionfish in a bright blue ocean swims near a red coral reef

Sirachai Arunrugstichai / Getty Images

Although humans have the ability to move fish from their native habitat to a new territory, it’s usually not a good idea. Sometimes the new habitat suits the invader so well that the results are catastrophic for local species. Ecosystems around the world have been dramatically altered as fish are shifted around, whether for commercial fishing stock or the aquarium trade. These species are some of the most hearty and adaptable, and therefore the most invasive on the planet. Most are so destructive that they are listed on the Global Invasive Species Database's list, "100 of the World's Worst Invasive Alien Species." Here are 10 fish species that are wreaking havoc around the globe.

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Walking Catfish

Side view of a walking catfish with whiskers.

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The walking catfish is an extraordinary species. Native to Southeast Asia, it is able to "walk" on dry land using its fins and tail to wriggle its way from one body of water to another. The species was introduced in Florida in the 1960s, and has been spotted in California, Nevada, Connecticut, Massachusetts, and Georgia. Because of its mobility, this opportunistic feeder finds its way into stock ponds and feasts on the fish being raised there. Fish farmers have been forced to place fencing around their ponds to keep the fish from eating up their entire stock.

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Common Carp

large common carp caught by fisherman

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This enormous freshwater fish is considered vulnerable to extinction in the wild, and yet it's also one of the most widely distributed and invasive species in the world. Common carp, which are native to Europe and eastern Asia, are found everywhere except the North and South poles and northern Asia. They feed by rooting through bottom sediments, destroying submerged vegetation and habitat for other species, and promoting algae growth. They also eat the eggs of other fish, causing native fish populations to plummet.

The species is so widespread and yet so destructive that ingenious ways of eradicating them have been devised, including introducing bluegils to consume carp eggs, deliberately exposing them to a deadly koi herpes virus, and using pheromones to locate carp so they can be removed.

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mosquitofish swimming with green plants behind it

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Mosquitofish are both celebrated and reviled. The fish, which is known for eating large quantities of mosquito larvae, was first introduced as a form of mosquito control. However, mosquitofish populations themselves are difficult to control and they aggressively compete with native species for food. They feed on a variety of small insects and insect larvae as well as zooplankton. In many areas where they have been introduced, they are less effective at mosquito control than native species. In these cases, mosquitofish benefit mosquitoes by reducing predation by the other species that eat mosquito larvae.

Researchers working to control the population growth of these invasive fish have devised a robotic largemouth bass to frighten the mosquitofish in an attempt to lower their fertility rate.

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Nile Perch

Side view of a Nile perch swimming in water with rocks below

Daiju Azuma / Wikimedia Commons / CC BY-SA 4.0

The Nile perch, native to Ethiopia, has had a devastating impact in East Africa where it was introduced in 1962. In Lake Victoria, the Nile perch has driven more than 200 native species of fish to extinction. The Nile perch eats everything from crustaceans and mollusks to insects and other fish. A single female can produce as many as 15 million eggs at once, so it doesn't take much time for the species to take over an area. The disastrous effects the Nile perch have caused placed it firmly on the list of one of the 100 worst invasive species in the world.

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Brown Trout

a spawning brown trout in shallow water with rocks below

Jay Fleming / Getty Images

This trout species may be a favorite among fishermen, but it's not necessarily a favorite among other fish. Brown trout are originally native to Europe, North Africa, and western Asia, but today they can be found all over the world. Not only does the brown trout compete — and usually win — against native trout species such as brook trout and golden trout, but it also competes with other species of fish, driving them out and altering the ecosystem. Conservation measures, including isolating brown trout from native species, are important steps in battling this invasive species.

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Rainbow Trout

a school of rainbow trout near the bottom of a rocky waterway

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The rainbow trout is another popular fish that is problematic in areas where it has been introduced. Rainbow trout is native to the western United States but like its brown trout counterpart, it can now be found all over the world. It's an adaptable predator that can out-compete many other species, driving some, like the California golden trout and humpback chub, to the edge of extinction. They can easily populate streams and cause a shift in invertebrate populations, which in turn has an impact on every other species that feeds on invertebrates.

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Largemouth Bass

A largemouth bass swimming in its natural freshwater habitat

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Another favorite of anglers, the largemouth bass has made its way around the world because of the excitement of catching them. A native of eastern North America, the largemouth bass has been introduced in Europe, Asia, Africa, and South America. Largemouth bass are carnivorous and feed on crayfish, sunfish, insects, frogs, and other largemouth bass. Their big appetite and position at the top of the food chain means that other native fish species where they are introduced are driven to extinction.

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Mozambique Tilapia

A school of Mozambique tilapias swimming near the bottom of their habitat

Greg Hume / Wikimedia Commons / CC BY-SA 3.0

Another member of the 100 worst invasive species is the Mozambique tilapia, a native of southeastern Africa. A hearty fish, they are resistant to temperature and salinity levels, and have been successfully introduced in over 90 countries on five continents. When released into new habitats, either intentionally or unintentionally, the Mozambique tilapia tends to take over. It's an omnivorous species that can eat everything from plants to small fish. In the U.S., introduction of this species is responsible for the decline of the desert pupfish in the Salton Sea, which is now an endangered species, and Hawaii's striped mullet.

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Northern Snakehead

A Northern snakehead fish with blotchy spots in water with a rocky bottom

Brian Gratwicke / Flickr / CC BY 2.0

Originating from China, Russia, and Korea, snakeheads are a tough, hardy fish at the top of the food chain that lack natural predators in introduced locations. Four species of snakehead fish have been introduced in the United States, and the Northern snakehead has established breeding populations in the wild. The snakehead can breathe air and can live out of water for up to four days, provided it stays wet. Because they will eat anything from fish, frogs, and crustaceans to small insects, they can cause significant disruptions in any ecosystem they enter and native species often lose out to this predator. The damage they've done is extensive; since 2002, it has been illegal to possess a live snakehead in the United States.

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Red lionfish swimming along the reef in a bright blue ocean

atese / Getty Images

Lionfish are considered one of the most aggressively invasive species in the world. Native to the waters of the Indo-Pacific and the Red Sea, two species of lionfish have established themselves in the Western Atlantic, Pterois volitans and Pterois miles. Lionfish are known for their long fins equipped with venomous spikes and their insatiable appetite. The combination puts it at the top of the food chain, with few natural predators in their invasive habitat. They threaten already-fragile reef systems and commercially important fish species such as snapper, grouper, and sea bass.

In order to try to control these predators, boaters and divers in Florida are encouraged to safely remove any lionfish they encounter.

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