The Worst Species of Invasive Fish

These fish species are highly aggressive when introduced to new habitats.

An invasive species is any life form that could end up spreading too fast and too wide when it is introduced to a new location. This can pose a danger to the environment, the native animals, plants, and the human settlements. This kind of domination causes a struggle for resources, space, and the destruction of biological diversity. Some species of fish have been known to be highly aggressive when introduced to new habitats, some feeding on the native species to extinction. Some of the worst invasive species of fish include the following.

8. Clarias batrachus

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Commonly known as the Walking Fish, this is a freshwater catfish that originates from Southeast Asia, it measures 1.6 feet long and weighs about 2.6 pounds. Its diet consists of mollusks, smaller fish, aquatic weeds, and other invertebrates. Clarius batrachus is a voracious eater, a trait that has made it an invasive species. The fish was introduced to fish farms in Florida in the 1960s after being imported from Thailand for aquaculture trade. Some of the fish escaped and integrated into the adjacent water bodies, by the time a ban was placed on the importation of the walking fish in 1968 the species had already invaded fish farms and ponds where they fed of the stocks reared by farmers.

7. Cyprinus carpio

Also referred to as the common carp, Cyprinus Carpio is a freshwater fish native to Europe and parts of Asia; the common wild carp is much smaller than the domesticated ones which can grow up to 47 inches long and weigh about 88 pounds for a full grown adult. Their diet consists of aquatic plants, insects, crustaceans, and benthic worms. Cyprinus carpio has been introduced to some 59 countries around the world with varying degrees of disasters. They are known to uproot aquatic plants destroying the direct food source for other animals like the Canvasbacks ducks. In South Australia, the quantity of the fish is much that fishers can no longer keep up. It is now illegal to release the common carp into the wild

6. Gambusia affinis

#6 Gambusia affinis

The western mosquitofish is another freshwater fish native to Illinois and Indiana that can reach lengths of about 2.8 inches. Their diet consists of small insects, zooplankton, and insect larvae. It is their affinity for eating mosquito larvae that were the reason behind their introduction to different habitats around the world as a biocontrol. This, however, affected other species as they outcompete other fish species that also feed on mosquito larvae. In California, the fish is only distributed to farmers with ponds with instructions not to release it to the wild. Gambusia affinis reaches sexual maturity fast, 43 days for males and 28 days for the females, and this is the reason behind their rapid reproduction.

5. Lates niloticus

The famous Nile perch is a freshwater fish found in most African rivers especially the vast Nile River. The fish is an essential source of food on the continent, and there have been attempts to introduce it to many other parts for fish farming with varying results. The Nile perch grow to 7 inches long and can weigh up to 440 pounds. Its diet consists of crustaceans, insects and other fish including those from their species. The fish was introduced to Lake Victoria in the 1950s and was responsible for the extinction of hundreds of native fish species. Owing to its high-fat content the process of smoking the Nile perch requires a lot of firewood which in turn causes deforestation of the neighboring areas.

4. Micropterus salmoides

#4 Micropterus salmoides

The largemouth bass is a freshwater fish native to North America found specifically in Georgia, Mississippi, and Indiana. The largemouth bass can grow up to 29 inches long and weigh about 25 pounds with an average lifespan of 16 years. It feeds on small fish, shrimps, snails, frogs, snakes, salamanders, bats, small water birds, and baby alligators. The fish was introduced to many parts of the world; for instance, in Guatemala the largemouth was responsible for the extinction of the Atitlan Grebe, a large water bird native to the place. It is also responsible for the reduction in the population of the bitterling fish in Japan. Their strong appetite and their ability to adapt to a new diet are what make them a dangerous invasive species.

3. Oncorhynchus mykiss

Commonly called the rainbow trout, this is a native of North America and Asia that lives in the cold tributaries of the Pacific. The adult trout can weigh up to 5 pounds with multi-colored bodies that range from blue-green to olive green in other species. The rainbow trout will eat anything to survive; their diet consists of insects, fish eggs, crustaceans, smaller fish, and shrimps. Oncorhynchus mykiss is reared in fish farms under close management to avoid them going into the wild.

2. Oreochromis mossambicus

#2 Oreochromis mossambicus

The Mozambique tilapia is native to Southern Africa. The adult tilapia can reach lengths of up to 14 inches and weigh about 2.5 pounds with a lifespan of about 11 years. It feeds on invertebrates, aquatic vegetation and zooplankton. The fish has been introduced in many parts for biocontrol as they feed on mosquito larvae, and this has led to the reduction of other fish populations in those areas as they cannot compete with the Mozambique tilapia. In Hawaii, the fish has pushed the native Mugil cephalus to the brink of extinction. It is also responsible for the accelerated decline of the desert pupfish in California.

1. Salmo trutta

The brown trout is a fish native to Europe that has both freshwater and ocean water species. The brown trout can grow for up to 39 inches long with a weight of about 44 pounds. Their diet is made up of invertebrates and other fish species, and its diet changes as it grows. The fish has been introduced to North America, South America, New Zealand, and Australia with some negative impacts. In Scotland and Ireland, the brown trout is responsible for the decline of the sea trout. The brown trout is also known to carry sea lice which cause diseases to other fish species.

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