Clarias Catfish: Walking Catfish ID, Hybrids, Eating

Yes. Clarias is a genus of catfish in the family Clariidae, the airbreathing catfishes of Africa and Asia. They have a long body, very long dorsal and anal fins, whisker-like barbels and an extra breathing organ built from modified gill arches that lets them take air at the surface (Wikipedia; FishBase). The species most people mean by 'clarias catfish' are the Asian walking catfish, C. batrachus, and the much larger African sharptooth catfish, C. gariepinus, which is farmed around the world.

• No adipose fin: this separates it from North American catfish such as channel and blue catfish (Wikipedia)
• Very long dorsal fin of 60-76 soft rays and a long anal fin of 47-58 rays, with no spines in either (FishBase)
• Pectoral fin spine: rough and serrated (FishBase)
• Head: a roughly triangular bony point at the back of the head (the occipital process), about twice as long as wide (FishBase)
• Colour: grey or grey-brown with small white spots along the sides (Wikipedia)

If you catch a catfish in Florida with a very long dorsal fin and no adipose fin, compare it with our channel catfish and brown bullhead pages before deciding.

• Walking catfish, C. batrachus: native to Java according to Wikipedia and FishBase, though USGS gives a wider Southeast Asian range; 47 cm and 1.2 kg (FishBase). Wikipedia notes that three closely related, more widespread species have often been confused with it, which is one reason range and size figures differ
• African sharptooth catfish, C. gariepinus: native to Africa and the Middle East; up to 1.7 m and 60 kg, adults usually 1-1.5 m (Wikipedia). Farmed worldwide because it grows fast on farm by-products at high densities
• Bighead or broadhead catfish, C. macrocephalus: Southeast Asia; males up to 120 cm; recognised by a short, rounded occipital process and white spots on a dark body (Wikipedia)

Size is where sources clash most. Practical Fishkeeping says C. batrachus 'officially' exceeds 1 m and cites an anecdotal 66 kg fish, while FishBase gives 47 cm and 1.2 kg. Figures that large fit C. gariepinus much better, so treat giant 'walking catfish' reports with caution.

'Hybrid catfish' in Clarias farming means a cross between two species rather than a separate wild fish:

• Thai hybrid: female C. macrocephalus crossed with male C. gariepinus. It grows faster than the native bighead catfish, and Wikipedia describes escaped hybrids as a threat to native stocks through competition and genetic mixing
• Heteroclarias: C. gariepinus crossed with Heterobranchus longifilis in Africa. These hybrids cannot reproduce and have white meat that consumers prefer, but are more easily stressed (Wikipedia)

A pure Clarias species breeds true; a hybrid is produced in hatcheries for faster growth or better meat. Telling them apart by eye is hard; head shape and the occipital process are the usual starting points.

Very. Practical Fishkeeping describes C. batrachus as extremely aggressive, a fish that 'will not back down' and will fight cichlids and other catfish, and advises no tank mates other than other Clarias. Young fish eat insects; adults take smaller fish, fry and eggs, dead or alive. In the wild USGS records heavy predation on native fish in drying pools in Florida, and fish farmers there have built fences to keep walking catfish out of their ponds.

Handle them with care: Practical Fishkeeping says the spines at the front of the dorsal fin and on the pectoral fins deliver a sting it compares to 'the worst bee sting', and that stings from African species have put people in hospital. Seek medical help for a sting that swells badly or will not stop hurting.

They are an important food fish. Wikipedia says the walking catfish is an affordable source of protein in Southeast Asia, served in Indonesian dishes such as pecel lele and mangut lele and grilled or fried in Thailand; FishBase notes it is sold live, fresh and frozen. The African catfish usually sells for more than tilapia (Wikipedia), and the bighead catfish is farmed in Thailand for its eating quality. As with any wild-caught fish, check local consumption advisories for the water it came from, and follow your area's rules on possessing live fish.

The walking catfish moves over land by wriggling like a snake while bracing on its pectoral fins, and its air-breathing organ lets it survive out of water for hours (Wikipedia). In Florida it spread through canals and over land, usually on rainy nights (USGS). It was imported in the early 1960s, escaped from fish farms in the mid-1960s and has been established in Florida since 1965; it failed to establish in California, Connecticut, Georgia, Massachusetts and Nevada, and cold snaps cause die-offs that limit its spread north (USGS).

The US Fish and Wildlife Service lists it as injurious wildlife (USGS), and Practical Fishkeeping notes Clarias are increasingly banned elsewhere too. Check your state or country's rules before buying one, and never release one into the wild. If you catch one in Florida, check FWC guidance on nonnative fish before deciding what to do with it.

The African catfish is Clarias gariepinus, the African sharptooth catfish, a large air-breathing catfish native to most of Africa and the Middle East (Wikipedia). FishBase calls it the North African catfish and describes its range as almost Pan-African, missing only from the Maghreb and the Cape; in Indonesia it is sold as lele dumbo (Wikipedia).

• Size: up to 1.7 m and 60 kg; adults usually 1 to 1.5 m (Wikipedia), while FishBase gives a common length of 90 cm. Maximum age 15 years (FishBase)
• Head and mouth: a flat, bony head and a broad mouth with four pairs of barbels (Wikipedia); two black bands along the lower side of the head (FishBase)
• Fins: a very long dorsal fin of 61 to 80 rays and an anal fin of 45 to 65 rays; only the pectoral fins carry spines, and the pectoral spine is serrated on its outer edge (Wikipedia; FishBase)
• Colour: dark grey or black on the back fading to a white belly (Wikipedia)
• Gill rakers: 24 to 110, increasing with size, a count FishBase uses to separate it from similar Clarias

It lives in lakes, rivers and swamps and even in sewage systems and oxidation ponds, breathes air with organs built from modified gill arches, crawls over dry ground to escape drying pools and can survive in mud between rainy seasons (Wikipedia).

Yes, they can sting. A study in the Annals of Agricultural and Environmental Medicine (Satora and colleagues, 2008) describes the venom apparatus of Clarias gariepinus as a single sharp, stout spine in front of each pectoral fin that can be raised and locked. The same paper reports 17 envenomation cases recorded by Polish toxicology centres from this species and the Asian stinging catfish, with intense pain, numbness, dizziness, swelling and redness, and in some cases a fast heart rate, weakness and low blood pressure; the authors note that infection is the most serious long-term complication. Stings are not unique to this fish: a 2009 study by Jeremy Wright, then a graduate student at the University of Michigan, estimated that at least 1,250 and possibly more than 1,600 catfish species may be venomous.

If you are stung, get medical care, especially if pain is severe, the wound swells or you feel faint, and tell the doctor it was a catfish spine so they can check for fragments and infection.

On published maximums, the African sharptooth catfish is the largest: up to 1.7 m and 60 kg (Wikipedia; FishBase). Its main rival is the vundu, Heterobranchus longifilis, which reaches 1.5 m and 55 kg and is called the largest true freshwater fish in southern Africa (Wikipedia). The two are close relatives, and farms in Africa cross them to produce the Heteroclarias hybrid described above.

Clarias gariepinus was introduced around the world for aquaculture from the early 1980s and is now found in Cuba, Hispaniola, Brazil, Vietnam, Indonesia, Taiwan and India (Wikipedia). FishBase marks it as a potential pest and notes adverse ecological impact in some places where it was introduced. It eats almost anything, from insects, snails and fish to reptiles, small mammals and waterbirds such as the common moorhen (Wikipedia), which is why an escaped population is hard on native wildlife.

In a fish shop, 'African catfish' usually means much smaller fish than Clarias. Aquarium Glaser, a German wholesaler, lists African catfish groups including:

• Synodontis squeakers: more than 133 species, from 6-7 cm to 60-70 cm, including the upside-down catfish, Synodontis nigriventris
• Pygmy squeakers, Microsynodontis: mature at just 3 to 4 cm
• African glass catfish, Parailia pellucida: transparent, up to about 15 cm
• Electric catfish, Malapterurus: produce electric discharges for defence and hunting

A Clarias gariepinus is not an aquarium fish for most homes: it grows past 1 m and eats tank mates. A photo in FishLens will tell you which kind of 'African catfish' you have.