Even our pristine Corkscrew Swamp Sanctuary isn’t immune to the influx of non-native fishes that have moved into South Florida in recent decades. Currently, Southwest Florida is home to at least 17 species of non-native freshwater fishes. Most of these species have entered Florida as aquarium pets, while others were brought here to farm as exotic delicacies.

Often released (either accidentally or intentionally) into neighborhood canals or ponds, the localized flooding we experience during heavy summer rains coupled with South Florida’s extensive canal system allow these opportunistic fish to move long distances relatively easily. Our interconnected waterways have allowed (and continue to allow) non-native fish to reach Southwest Florida from the large port cities north and east of us. Unfortunately, Tampa and Miami/Ft. Lauderdale are currently home to at least 23 additional non-native freshwater species that, in time, can potentially move into our area.

The non-native fish species that do especially well here are from tropical areas of Asia, Africa and Central and South America. These species (many of which are from the family of ‘cichlids’) are so well-adapted to our harsh aquatic environment that studies have shown some of them are better able to survive our dry-season, low oxygen conditions than our native fishes. Many of the non-natives are also larger and notably more aggressive than our native fishes. Studies conducted by Audubon biologists and others have shown marked decreases in native fish populations as non-native fish spread.

The proverbial chink in their armor, however, appears to be our winter cold spells. In addition to the manatees and snook that made news headlines, the record-breaking cold temperatures we experienced last January were responsible for killing a disproportionate number of non-native freshwater fish. In fact, Audubon’s monitoring efforts in Big Cypress National Preserve have noted a marked absence of non-native fishes at several study sites since the January 2010 cold snap. Unfortunately, scientists anticipate the non-native fish population will quickly recover - perhaps even evolving more cold tolerance through time.

Because there are currently no effective methods of controlling the spread of non-native fishes once they become established, our native ecosystem is relying on us to stop the introduction and spread of these, and all non-native animals. As we learn from the consequences of Burmese pythons in the Everglades and Nile monitor lizards in Cape Coral, the importance of responsible pet ownership has never been more apparent here in Southwest Florida.

Article by Dr. Shawn Liston.