Walking Catfish (Clarias batrachus)

It’s a rule that any fish with the word ‘walking’ in its name is automatically nominated for a post in this blog. Walking is just not something fish do (except for the Red-Lipped Batfish, which I wrote about earlier). So when I saw the name walking catfish in one of my many books on animals, I had to find out more.

The walking catfish is native to southeast Asia, and is found in a wide range of countries, as far west as Pakistan. The fish has been introduced to Florida, where it is now a pesky invasive species. The spread of the walking catfish in Florida is quite remarkable – the species was introduced in only one or two places in the state, and within ten years had spread to twenty counties.

A diagram showing the spread of the walking catfish in Florida.

A diagram showing the spread of the walking catfish in Florida.

So what makes the walking catfish such a successful invader? There are two key adaptations that contribute to the fish’s prowess as a pest. One is modified pectoral fins. The fins have very tough spines embedded in them, and when the catfish extends them and wiggles its body back and forth, it can ‘walk’ across land. It’s not a very graceful way of moving, but I doubt the catfish cares.

The second adaptation is that the walking catfish breathes air. This gives it two very important benefits: 1) it can live in brackish, hypoxic waters that are unsuitable for many other fish, and 2) it can survive outside of water as long as it stays moist. This lets the fish abandon a pool that is about to dry up, which helps when most of your habitat consists of temporary pools of water. The catfish is able to breathe water thanks to something called the suprabranchial arborescent organ. The organ helps support gill filaments that normally would collapse without water to keep them afloat.

A walking catfish enjoying some time on land.

A walking catfish enjoying some time on land.

Walking catfish spawn in the rainy season, presumably when food is at a peak. The catfish build a nest out of vegetation and submerged waste. Males are in charge of guarding the young, doing so when they are eggs and after hatching. The young are reproductively mature after a year. Walking catfish in its native range can reach up to 61cm, while in Florida ‘large’ specimens are usually around 36cm. I have no idea why they’re so much smaller in Florida; maybe the introduced population was composed of unusually diminutive fish.

Asides from being used for food, walking catfish have also been frequently kept as pets. I don’t think I would want one – fish aren’t really my thing. Also, it’s illegal in Florida to own walking catfish, so if you live there don’t try and get one for a pet. Just some friendly advice!

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