DESCRIPTION: Asian swamp eels are not true eels. Swamp eels have a scaleless, elongated body with a tapering tail and blunt snout. Their teeth appear like bristles and they have one V-shaped gill located beneath the head. Swamp eels are sometimes mistaken for native American eels (Anguilla rostrata), although American eels differ in that they have pectoral fins, rayed dorsal, anal and caudal fins, and scales (although embedded). Swamp eels may also be mistaken for lamprey, but these latter fish have no jaws and have ovoid mouths; lampreys also have distinct dorsal and caudal fins and 7 gill openings on each side. The life cycle of the Asian swamp eel takes place solely in freshwater. All young are females. Some females develop into males as adults, however, males can change back to females if female densities are low. The change from one sex to the other can take up to a year. Reproduction can occur throughout the year. Eggs are laid in bubble nests located in shallow waters. These bubble nests float at water’s surface and are not attached to aquatic vegetation. The swamp eels preferred environment includes a wide variety of freshwater habitats: shallow wetlands, stagnant waters, marshes, streams, rivers, ditches, canals, lakes, reservoirs, and ponds in depths of <3 m. Swamp eels appear to tolerate cold temperatures well (successfully established in areas where temperatures fall below freezing) and are able to tolerate wide range of water oxygen levels; if not using gills underwater, they can obtain up to 25% of oxygen from air cutaneously (through their skin). Swamp eels prefer freshwater habitats, but can tolerate brackish and saline conditions.

PATHWAYS/HISTORY: Asian swamp eels are native to Asia, from northern India and Burma to China. They were probably introduced to North America by aquarium release, stocking as a food source, or escaped from fish farms during flooding events. Swamp eels have established populations in Florida, Georgia, and Hawaii on the island of Oahu.

RISKS/IMPACTS: Asian swamp eels eat a broad range of prey, including fish, shrimp, crayfish, frogs, turtle eggs, and aquatic invertebrates (e.g., worms and insects). Although the ecological impacts in North American waters are relatively unknown, some impacts are documented in other regions of the world where they have become established. Swamp-eel competition may displace native aquatic species. They may accelerate the drying of shallow water bodies (when the species is abundant) during periods of drought via their extensive borrow system, thereby causing additional risk to other aquatic organisms. On the positive side, swamp eels are used as food source in many Asian cultures. Significant adverse impacts have yet to be documented, but due to its predatory nature, the Asian swamp eel appears to have the potential for adverse environmental impacts in North America. There is concern, for example, that they may disrupt the Everglades National Park ecosystem.

MANAGEMENT: Control Measures currently being evaluated include a combination of electrical barriers (to deter movement), vegetation removal, and trapping to assist in limiting dispersal. Electroshocking is used for collection.

WHAT YOU CAN DO: Do not release of bait into a water body or transport bait from one water body to another (it is suspected that juveniles have been used as bait material). Do not release any aquarium fish into local waters. Do not intentionally stock these fish.

PROFILE CREDIT: USGS - IMAGE CREDIT: USGS