Invasive Fish: Our Unwanted Denizens of the Deep

 By Bob Davidsson

        Reef fish with poisonous fins, a catfish that walks on land and a variety of fugitives from home aquariums are examples of the many invasive species of fish that are thriving in our coastal waters, lakes and canals in South Florida.

        The U.S. Geographic Survey defines invasive fish as any species living outside of its normal range with the potential to damage the local environment, economy or public health. Section 68-5.007 of the Florida Administrative Code says "No person shall import to the state, sell, possess or transport... prohibited nonnative species."

        The main sources of invasive fish in Florida are home aquariums. When tropical fish  become too large or numerous for a fish bowl, pet owners believe they are being merciful to their aquatic pets by releasing them in a neighborhood pond or canal.

        Unfortunately, most brightly colored tropical fish are soon consumed  by predatory fish or  birds. Those that survive and thrive in our warm subtropical waters often become pests by crowding the habitat of native species and outcompeting them for food.

        Some of the  nonnative invasive fish that have negatively impacted their local aquatic environments are profiled below:

The Lionfish

        The environmental aquatic enemy number one on Florida's reefs and coastal waters is the lionfish. It is a carnivorous fish with a voracious appetite that was native to the South Pacific and Indian Oceans.

        The first lionfish was reported in South Florida coastal waters in 1985. It is a popular ornamental fish in saltwater aquariums which quickly extended its range throughout the Caribbean and eastern coast of the United States once freed from the confinement of a fish tank.

        The lionfish has no natural predators due to its protective poisonous  fins. In coastal reef environments, it competes with native game fish like snappers and groupers. The lionfish feeds on 50 species of reef fish, and one female can release up to two million eggs each year.

The Walking Catfish

        Walking catfish are natives of southeast Asia. The nonnative species was introduced to Florida in the 1960s when they made their escape from aquaculture facilities. Their range has expanded throughout southeast Florida.

          The catfish received its name from its ability to wiggle across the land from one body of water to another in search of food or a better habitat. Their strong pectoral fins and long snakelike bodies allow them to slither on land. A special gill structure enables the catfish to breath air during their terrestrial journeys.

         The walking catfish is an omnivore that feeds on smaller fish, their eggs and larvae as well as plants. It is listed as an invasive species  by the Florida Fish and Wildlife Conservation Commission, and a permit is required to buy, sell or trade the nonnative fish.

 Bull's-eye and Northern Snakeheads 

       Snakeheads first appeared in the ponds and canals of Broward County in the year 2000. They are native to southeast Asia, where they are prized as a game and food fish. However, in South Florida, snakeheads are apex predatory fish feeding on native species.

        Snakeheads are distant relatives of native bowfins (mudfish), and they can breath air in low oxygen ponds or on land for short periods of time. The torpedo-shaped predators feed on native fish, and supplement their diets with crayfish, frogs, snakes, insects and turtles.

        Some fishermen prize the snakehead as a game fish,  but they should be handled with great care. They have a nasty bite that may become easily infected.

Cichlids and Tilapia

        There are 25 varieties of nonnative  tropical cichlids and related tilapia homesteading in South Florida waterways. Most can trace their nautical ancestry to South America and Africa. 

         They were introduced to Florida waters in the usual manner - released from home aquriums with the assistance of their human owners.  They are small but aggressive fish that vigorously defend their nests. They tend to crowd out native sunfish from their spawning sites through their large numbers, and unique "mouth breeding" technique of providing a refuge for their young when threatened  by a predator. 

        The State of Florida introduced the peacock bass to Lake Okeechobee, Lake Osborne and other South Florida lakes to help control invasive species. It is a rare example of a successful introduction of a nonnative species. Peacock bass feast on cichlids and tilapia. The bass also is popular with fishermen as a game fish.

The Monster of the Caloosahatchee

        In March 2021 fishermen found the remains of a arapaima floating near the mouth of  the Caloosahatchee River in Lee County. Magazines and newspapers across the nation had a field day reporting on Florida's newest monstrous invasive species.

        After the headlines faded, the mystery remains. How did a native species from the Amazon basin in  South America arrive in South Florida. More important, is there a breeding population of arapaimas in the Caloosahatchee and its interconnected waterways of Lake Okeechobee, the Kissimmee River, and east coast waterways by way of the St Lucie C-51 and Hillsboro canals?

        The arapaima has survived and thrived unchanged for five million years. In addition to  being, the world's largest freshwater predatory fish, the arapaima has large scales on its sides that act as body armor.

        The 400-pound arapaima has a varied diet consisting of  fish, lizards, small birds and mammals. The air-breathing omnivore also feeds on aquatic plants and any nuts or seeds within its reach.

The U.S. Wildlife Service reported in 2019 that "there are no established populations of arapaimas in the United States." However, the report did not deny the existence of arapaimas in Florida.

        The arapaima is classified as a "conditional species" in the State of Florida. That means a permit is required to keep one.  People who choose to collect or display the giant fish are instructed to confine it to a private tank. At least that is the hope.

        It remains unknown if arapaimas will join a growing list of predatory invasive species in Florida that includes Burmese pythons African monitor lizards, iguanas and aggressive tagu lizards from South America.*

c.) 2021. Davidsson.   

*NOTE: Article was reprinted in South Central Florida Life publications. Read also the April 2015 article titled "Alien Species Find Home in the Palm Beaches" archived in Older Posts.