Why Eel Catfish Swim in Massive and Mesmerizing Schools

It never ceases to amaze us how many sea creatures remain unknown or unseen by most people. The ocean is incredibly vast, with much of it still undiscovered, which is why this is likely your first introduction to the eel catfish. That’s a shame because, as you’ll see in this YouTube video, eel catfish are marvelous creatures, especially when swimming in large groups.

But why do they do that? Let’s dive deep into the world of eel catfish and their particular behaviors. 

What are Eel Catfish?

The video shows us a school of striped eel catfish (Plotosus lineatus). You’ll often find them swimming alone or in schools near tide pools, coral reefs, and estuaries along the coasts of the Indo-Western Pacific, including areas near Australia, Japan, and the shallow waters of Pacific islands. 

You can identify an eel catfish by the stripe running along its body, which is especially distinctive in juveniles. It’s clear that they’re a type of catfish when you see the four sets of barbels near their mouths. The barbels may look like whiskers, but they are actually highly developed sensory organs that help the fish track down food and prey. This variety of catfish can grow up to 12 inches long and appear eel-like. Their stripes are usually prominent, appearing white or yellow against a darker body.

Do They Always Swim in Schools? 

A group of eel catfish is called a school. Eel catfish don’t always swim together, but it’s common to see them in a similar formation to what you saw in the video. The school will often include at least 100 fish. The primary reasons why they swim in schools are for protection (since they’ll look like a larger organism) and to find food. 

As you can see in the video, the way they swim in the school is quite unique. The spherical shape forms because fish at the top of the school switch places with those at the bottom, and vice versa. That way, the fish can take turns watching for predators and looking for food. This behavior is more common among the younger fish. As they get older, they usually separate from the group and go solo or form smaller groups of about 20 fish.

Eel catfish prey on small fish, worms, and various invertebrates. They find their food by first smelling it along the seafloor and then using the barbels on their faces to stir up the sand and uncover prey.

It’s a School You Don’t Want to Attend

The school of eel catfish in that video is absolutely stunning, but it’s a sight you want to view at a distance. In addition to their striking appearance, eel catfish have a unique defense system: venomous spines along their pectoral and dorsal fins. When agitated, the fish use these spines to inject venom, which can cause severe pain, swelling, and even temporary paralysis. There are no confirmed cases of the venom being fatal to humans, but individuals should seek medical attention if stung.

As children, we often hear about schools of fish in science class, but it’s truly remarkable to see them in action with your own eyes. This remarkable video is another example of how nature can take our breath away.