Clarias batrachus a voracious predator native to southeastern Asia has been introduced into many places for fish farming. Walking catfish, as it is commonly known (named for their ability to move over land), is an opportunistic feeder and can go for months without food. During a drought large numbers of walking catfish may congregate in isolated pools and consume other species. They are known to have invaded aquaculture farms, entering ponds where they prey on fish stocks. C. batrachus has been described as a benthic, nocturnal, tactile omnivore that consumes detritus and opportunistically forages on large aquatic insects, tadpoles, and fish.
Description Clarias batrachus has a broad, flat head and an elongate body which tapers toward the tail. It is readily recognizable as a catfish with four pairs of barbels whiskers and fleshy, papillated lips. The teeth are villiform, occurring in patches on the jaw and palate. Its eyes are small. The dorsal fin is continuous and extends along the back two-thirds of the length of the body but there is no dorsal spine. The dorsal, caudal, and anal fins together form a near-continuous margin; the caudal fin is rounded and not eel-like though it is occasionally fused with the other fins. Its pectoral spines are large and robust and finely serrate along the margins with which it walks accompanied by a back and forth flexion.Their coloration is olive to dark brown or purple to black above, blue green on the sides and white below, with white specks on their rear side. C. batrachus may be easily distinguished from many of the North American Ictalurid catfishes in that the walking catfish lacks an adipose fin (Masterson, 2007; Robins, undated; GSMFC, 2006).
Occurs in: estuarine habitats, lakes, water courses, wetlands
Habitat description Walking catfish can be found in a variety of habitats, but they are most commonly encountered in stagnant, muddy or swampy water of high turbidity. Known to inhabit medium to large rivers, swamps, ponds, ditches, flooded fields, rice paddies, and pools left in low spots after rivers have been in flood, it is also reported to occur in intercoastal waterways of salinities up to 18 ppt. It is a tropical species with a moderate tolerance to colder waters with a reported a lower lethal temperature of 9.8°C. During cold dry months, walking catfish burrow into the sides of ponds and streams where they remain dormant until the spring rains begin (Masterson, 2007; FishBase, 2003; GSMFC, 2006).
General impacts Clarias batrachus in South Florida are known to invade commercial aquaculture facilities, often consuming vast numbers of the stocks of fishes (Robins, undated). The impacts from this opportunist feeder are probably most pronounced in small, isolated wetland ponds where walking catfish quickly consume or outcompete other resident populations to become the dominant species in the pond. Resident centrarchids (freshwater sunfish) and native catfish species appear particularly susceptible to impacts from this invader (Masterson, 2007). C. batrachus can also negatively impact native amphibian populations by preying on tadpoles. The ability of walking catfish to exploit isolated, ephemeral water bodies allows them to access tadpole prey stocks that other fish cannot reach (Masterson, 2007).
Uses Fisheries: commercial, aquaculture: commercial, aquarium: commercial (FishBase, 2003). An important food fish that is marketed live, fresh and frozen. (FishBase, 2003)
Notes Clarias batrachus can survive out of water for quite sometime using its auxiliary breathing organs and move short distances over land allowing it to migrate to new water bodies (Froese and Pauly, 2009).
Geographical range Native range: Southeastern Asia including eastern India, Sri Lanka, Bangladesh, Burma, Indonesia, Singapore, and Borneo (FishBase, 2003). Known introduced range: Indonesia (Sulawesi), USA, Hong Kong, Taiwan, China, UK, Papua New Guinea, Guam, Taiwan, Thailand (FishBase, 2003). Probably introduced into the Philippines (Nico, 2005)
Introduction pathways to new locations Aquaculture: Introduced into Hong Kong from Thailand for aquaculture, (FishBase, 2003). For ornamental purposes: Introduced into the USA from Thailand and from Java, Indonesia for ornamental purposes, (FishBase, 2003). Pet/aquarium trade: The walking catfish was imported to Florida, reportedly from Thailand, in the early 1960s for the aquarium trade (Courtenay et al. 1986).
Local dispersal methods Aquaculture (local): Aquarium releases likely are responsible for introductions in other states of America. (Nico, 2005) Escape from confinement: In Florida adult fish imported as brood stock escaped from confinement, either from a fish farm in northeastern Broward County or from a truck transporting brood fish between Dade and Broward counties. (Nico, 2005) Other (local): Dill and Cordone (1997) reported that this species has been sold by tropical fish dealers in California for some time. (Nico, 2005) Water currents: In America dispersal apparently has occurred by way of the interconnected network of canals along the southeastern coastal region. (Nico, 2005)
Management information Preventative measures: Outside of its native range, numerous countries have banned possession of the Clarias batrachus, including the United States, which has classified all members of the family Clariidae as injurious wildlife which are illegal to possess without a federal permit (Robins, undated).
Nutrition Clarias batrachus feeds on insect larvae, earthworms, shells, shrimps, small fish, aquatic plants and debris.
Reproduction Clarias batrachus engages in mass spawning migrations in late spring and early summer. Inundated patty fields have been reported as favored spawning grounds over its native range. The pair manifests the 'spawning embrace' which is widely observed in other catfish species. Mating occurs repeatedly for as long as 20 hours. The pair gently nudge each other in the genital region and flick their dorsal fins; male wraps his body around the female, then the female releases a stream of hundreds to thousands of adhesive eggs into the nest or on submerged vegetation. Males guard the nests and embryos hatch in about 30 hours. Both parents guard fry for about three days, when they develop barbles visible to the naked eye and swim freely (GSMFC, 2006; FishBase, 2009, Ros, 2004c).
Lifecycle stages In southeast Asia, spawning period is during the rainy season, when rivers rise and fish are able to excavate nests in submerged mud banks and dikes of flooded rice fields (FishBase, 2003).
This species has been nominated as among 100 of the "World's Worst" invaders
Principal sources:Nico, L., 2005. Clarias batrachus Nonindigenous Aquatic Species Database, Gainesville, FL. FishBase, 2003. Species profile Clarias batrachus Walking catfish
Compiled by: Profile revision: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
