Clariidae - Labyrinth Catfishes
Albino juvenile walking catfishes were imported from Bangkok, Thailand, in the early 1960's for sale in the aquarium-fish trade. In the mid-1960's, adults--subsequently imported as brood stock--either escaped from culture facilities such as a large fish farm west of Deerfield Beach, in what is now the city of Parkland, Broward County (Courtenay et al. 1974) or from a truck transporting brood fishes between Miami and Parkland in Broward County, Florida (Courtenay 1979 b) in the mid-1960's. Releases in the Tampa Bay area, Hillsborough County, in about 1968 resulted in the establishment of at least one population (Courtenay et al. 1974; Courtenay and Miley 1975). In 1968, this exotic fish was confined to three Florida counties; by 1978 it had spread to 20 counties in the southern half of peninsular Florida--a profound feat for a fish (Courtenay 1978, 1979b). The species is capable of overland migrations that normally take place at night or during periods of rain. Reasons for these migrations have not been determined. During a fish kill of unknown origin in early 1976 near the Big Cypress Swamp, Collier County, almost 90% of the kill consisted of walking catfishes. This indicated that the fish is able under the right conditions to become a dominant species. As many as 3,703 kg/ha of walking catfish have been seined from some small natural ponds in Florida (Lachner et al. 1970). Abundances of that magnitude must affect the native species. No studies, however, have been conducted to measure the ecological or economic impacts of this species.
Shortly after the walking catfish became established, some tropical-fish farmers sustained losses when the walking catfish entered their ponds and destroyed their crops. The farmers' solution to the problem was to build 46-cm wire fences to keep the walking catfish out. These precautions were not effective when the ponds flooded. State extension agents now recommend that the fish farmers increase the height of the dirt berms around the ponds above the high-water elevation (Craig Watson, Aquaculture Extension Agent, University of Florida, personal communication). This construction has almost stopped all walking catfish predation on cultured fishes and reduced the loss of valuable tropical fishes from the walking catfish and flooding.
Environmentalists' concerns about the walking catfish in Florida depends on the area of Florida. In the southern part of the state where the fish has been present for many years, fishery personnel of the Florida Game and Fresh Water Fish Commission have little concern and, in fact, believe populations have declined greatly. However, the species has been reported as still extremely abundant in the Shark Valley and in the Anhinga Tracts of the Everglades National Park and is of local concern (C.R. Robins , Professor of Fisheries, University of Miami personal communication). In northern areas of the state where the finding of the species is still a novelty and where it is reported often, managers are concerned about its effect, but no studies of its effects in Florida have been initiated.
Studies of temperature tolerance in this species (Shafland and Pestrak 1982) indicated that cold water temperatures in winter do not limit the species from spreading much farther north than its present distribution near Orlando. Its habit of burrowing in mud during short periods of cold and its ability to survive in warm springs also allow it to survive in at least small numbers farther north than expected. This and all other clariid catfishes are on the Federal Injurious Species List (50 CFR Part 16) and therefore cannot be imported into this country without a federal permit.
Food-habit studies of this species indicate that its diet in southern Florida consists of 35% aquatic insects (Haliplus spp., dytiscid beetles, mayflies, dragonflies, other beetles), 18% fishes (Fundulus, Gambusia, and Lepomis), and 10% plant material (Courtenay et al. 1974). Waldners (1974) studies revealed similar food habits. In addition to benthic organisms, Ostracoda, Tendipedidea, Hyalella, and Brachyura, he found large amounts of detritus in the stomachs of walking catfishes. He concluded that the walking catfish is an opportunistic feeder and could compete with native fishes if the food supply was limited. Walking catfishes are sometimes found in the intracoastal waterway in salinities of 18 ppt. Success of this species has been attributed to its ability to survive in poorer water quality than most species of native fishes and its guarding of its young into even the free-swimming stages (Taylor et al. 1984).
