PlanetCatfish.com

This Saturday I was at work doing routine maintenance on some of our tanks, when I came across one of our striped raphael catfish. It was in a tank with quite a few others, though this was the only one out in the open. It was also not moving, and appeared to be dead. I reached into the tank to remove it, and grasped it firmly by the tail. What happened next was a total surprise! The fish was alive, and it seemed to be pretty irate! It suddenly began vibrating very quickly, and then released a cloud of some white substance!

Has anyone here seen or heard of this, and does anyone know what it is? I'd be interested to know exactly what kind of predator-defense system the fish used against me.

This is a typical doradid defense response.

Carl Ferraris mentions that doradids will exude a milky white fluid from their axillary pore (porus pectoralis) and has pictures of an Acanthodoras cataphractus doing so in his book (Catfish in the Aquarium).

Yup, that sounds like what happened. Out of curiosity though, how exactly does the fluid affect potential predators? Is it poisonous or repulsive, or does it just serve to confuse them?

It's probably either repulsive of poisonous. The axillary pore secretions are known to be poisonous in some catfish groups, and are said to taste like milk in others.