Walking catfish

Walking catfish
Conservation status
Not evaluated (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Siluriformes
Family:	Clariidae
Genus:	Clarias
Species:	C. batrachus
Binomial name
Clarias batrachus (Linnaeus, 1758)
Synonyms
Clarias assamensis Clarias punctatus Silurus 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 it is 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. 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

The 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 fins 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 due to its hidden embedded sting or thorn-like defensive mechanism hidden behind its fins (including the middle ones before the tail fin, like the majority of all catfishes).

Taxonomy, distribution, and habitat

The walking catfish is a tropical species native to 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 (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, with occasional trips to the surface to gulp air.

Diet

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, so it is particularly harmful when invasive.

As an invasive species

Within Asia, this species has been introduced widely. In the United States, it is established in Florida and reported in California, Connecticut, Georgia, Massachusetts, and Nevada and regarded as an invasive species.

The walking catfish was imported to Florida, reportedly from Thailand, in the early 1960s for the aquaculture 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 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

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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.

One of the most common freshwater catfish in the Philippines. Known as "Hito" in local language.

It is a delicacy in the Indian state of Assam, where it is called magur mas(মাগুৰ মাছ).

In Indonesia, it is called "lele".

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.

Aquarium

A white variation with black patterns is commonly seen in the aquarium fish trade. However, this color variation is also prohibited where walking catfish are banned. Very well-rooted plants and large structures that provide some shade should be included. Any tankmates small enough will be eaten.

See also

• Eel catfish
• List of freshwater aquarium fish species
• List of invasive species in the Everglades

External links

• Ros, Wolfgang (2004): "Clarias batrachus - Erfolgreiche Froschwels-Nachzucht im Aquarium", Datz 57 (7): 12-15.
• Ros, Wolfgang (2006): "Clarias batrachus - Auslösen der Fortpflanzung bei Froschwelsen", Datz 59 (4): 33-37.pam:Itu