Walking Catfish (Clarias Batrachus)

The walking catfish (Clarias batrachus) is a species of freshwater airbreathing catfish native to Southeast Asia, but also introduced outside its native range where considered an invasive species. It is named for its ability to "walk" across dry land, to find food or suitable environments. While it does not truly walk as most bipeds or quadrupeds do, it has the ability to use its pectoral fins to keep it upright as it makes a sort of wiggling motion with snakelike movements. It can survive using this form of locomotion as long as it stays moist. This fish normally lives in slow-moving and often stagnant waters in ponds, swamps, streams and rivers, flooded rice paddies or temporary pools which may dry up. When this happens, its "walking" skill allows the fish to move to other sources of water. Considerable taxonomic confusion surrounds this species and it has frequently been confused with other close relatives.

Characteristics and anatomy

Walking catfish has an elongated body shape, and reaches almost 0.5 m (1.6 ft) in length and 1.2 kg (2.6 lb) in weight. Often covered laterally in small white spots, the body is mainly coloured a gray or grayish brown. This catfish has long-based dorsal and anal fin as well as several pairs of sensory barbels. The skin is scaleless but covered with mucus, which protects the fish when it is out of water.
One main distinction between the walking catfish and native North American Ictalurid catfish is the walking catfish's lack of an adipose fin.
This fish needs to be handled carefully when fishing it out due to its hidden embedded sting or thorn-like defensive mechanism hidden behind its fins (including the middle ones before the tail fin, just like the majority of all catfish).

Taxonomy, distribution and habitat

The walking catfish is a tropical species native of Southeast Asia. The native range of true Clarias batrachus is only confirmed from the Indonesian island of Java, but three closely related and more widespread species have frequently been confused with this species. These are C. magur of northeast India and Bangladesh, a likely undescribed species from Indochina and another likely undescribed species from the Thai-Malay Peninsula, Sumatra and Borneo. The undescribed species have both been referred to as Clarias aff. batrachus. At present the taxonomic position of the Philippines population (where called hito or simply "catfish" by the locals) is unclear, and it is also unclear whether South Indian populations are C. magur or another species. As a consequence, much information (behavioral, ecological, related to introduced populations, etc.) listed for C. batrachus may actually be for the closely related species that have been confused with true C. batrachus. True C. batrachus, C. magur and the two likely undescribed species are all kept in aquaculture.
Walking catfish thrive in stagnant, frequently hypoxic waters, and are often found in muddy ponds, canals, ditches and similar habitats. The species spends most of its time on, or right above, the bottom surface, with occasional trips to the surface to gulp air.

Diet and eating habits

In the wild, this creature is omnivorous; it feeds on smaller fish, molluscs and other invertebrates as well as detritus and aquatic weeds. It is a voracious eater which consumes food rapidly and in this habit it is a particularly harmful invasive species.

As an invasive species

Within Asia, this species has been introduced widely. In the United States, it is an invasive species, which is now established in Florida and reported in California, Connecticut, Georgia, Massachusetts, and Nevada.
The walking catfish was imported to Florida, reportedly from Thailand, in the early 1960s for the aquarium trade. The first introductions apparently occurred in the mid-1960s when adult fish imported as brood stock escaped, either from a fish farm in northeastern Broward County or from a truck transporting brood fish between Dade and Broward counties. Additional introductions in Florida, supposedly purposeful releases, were made by fish farmers in the Tampa Bay area, Hillsborough County in late 1967 or early 1968, after the state banned the importation and possession of walking catfish. Aquarium releases likely are responsible for introductions in other states. Dill and Cordone (1997) reported that this species has been sold by tropical fish dealers in California for some time. They have also been spotted occasionally in the Midwest.
In Florida, walking catfish are known to have invaded aquaculture farms, entering ponds where these predators prey on fish stocks. In response, fish farmers have had to erect fences to protect ponds. Authorities have also created laws that ban possession of walking catfish.

As food

Sold in HAL market, Bangalore, India (unlikely to be the true C. batrachus; see text)

In Thailand, this fish is known as Pla Duk Dan (Thai: ปลาดุกด้าน). It is a common inexpensive food item, prepared in a variety of ways, being often offered by street vendors, especially barbecued or fried.
In coastal Karnataka, India, it is called Mugudu (Tulu: ಮುಗುಡು) and is considered a delicacy.
Neither Thai nor Indian populations are likely to be the true C. batrachus