Photographer: Wibowo Djatmiko Copyright: (CC BY-SA 3.0)
Clarias batrachus has a flat, broad head and an elongated body tapering toward the tail. It has a typical catfish appearance with four pairs of “whiskers” with a wide mouth and bristle-like teeth. The eyes are small and the dorsal fin is long and extends two-thirds of the body length. Each pectoral fin has a strong, rigid spine at the front that helps with “walking”. This terrestrial locomotion is achieved by using the pectoral spines to pull itself along while flexing the body back and forth. The scale less body is usually a drab gray or gray-brown with white flecks on the side. Albino and calico colors (orange, white and black) are common in the aquarium fishes. All of the original walking catfish introduced into Florida were albinos. The gills of the walking catfish are specially structured with tree-like organs to permit their breathing on land and in stagnant water. They usually reach lengths of about 12 inches but the largest reported one in the United States was 20 inches and weighed about 3 pounds.
Clarias batrachus are very strong reproducers and it was a big concern when they were first released. It was thought that they would out-compete native catfish species and spread rapidly. This hasn’t really been the case, there’s no physical evidence that these catfish are detrimental to native fish species. The impacts from this opportunist feeder are probably most pronounced in small, isolated wetland ponds where walking catfish quickly consume or out-compete other resident populations to become the dominant species in the pond. However, they do have an economic impact on fish farmers, who have to construct barriers just to keep them out of their aquaculture pond and are very unwanted because they are known to eat the fish and their eggs.
After one year walking catfish become sexually mature. Nests are hollowed out in submerged vegetation and are guarded by adults. Up to 1,000 eggs can be laid at one time and stick to the vegetation. Once the eggs have been fertilized, the male guards the nest and the female keeps intruders away. Embryos hatch about 30 hours and the fish fry stay under the protection of the parents for about 5 days.
This fish was first imported into Florida in the early 1960s from the aquarium trade and accidentally into local waters in the mid-1960s. Intentional releases by fish farmers occurred in 1967 and 1968 after Florida prohibited the importation and possession of walking catfish. 10 years after the first escapes they were found in over 20 counties in Florida, not they’ve been found in several other states.
India, Bangladesh over to Thailand
U.S. Habitat: Most commonly found in freshwater habitats in which most native species fo not thrive, Since they are bottom-dwellers they dominate in warm, muddy ponds, swamps, canals and ditches. Walking catfish kills have been documented in Florida when the temperatures get below 50oF
U.S. Present: AZ, CA, CT, FL, GA, MA and RI
Under the Lacey Act it is a violation of federal law to import these fishes into the United States without a permit. Some states have made it illegal to possess walking catfishes all together. Any walking catfish caught by anglers must be quickly killed. For fish farmers they have to spend the extra money to create fish fences to protect their aquacultures.
Baber M.J. and K.J Babbitt. 2003. The relative impacts of native and introduced predatory fish on a temporary wetland tadpoles assemblage. Oecologia 136:289-295.
Courtenay, W.R., Jr., Sahlman H.F., Miley W.W., II, and D.J. Herrema. 1974. Exotic fishes in fresh and brackish waters of Florida. Biological Conservation 6:292-302.
Shafland P.L. 1996. Exotic Fishes of Florida-1994. Reviews in Fisheries Science 4:101-122.
Woodward, Susan L., and Joyce Ann. Quinn. 2011. Walking Catfish. Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels. Santa Barbara, CA: Greenwood, 198-200. Print.