In this clip taken in Jemeluk Bay, Bali, by the Abyss Diving Center, we see a school of juvenile striped eel catfish demonstrating a fascinating defensive behaviour.
As striped eel catfish at the bottom forage and eat, the ones up top keep a lookout for predators and other dangers. The Diving Center explains:
“These little guys tend to form a school as juveniles, up to a hundred individuals, to protect themselves from predators, and go about their lives on their own when they reach their sexual maturity. Fun fact, if the adults are venomous and can inflict a painful sting, the young ones can only produce a mild version of the venom, tingling the fingers of the people putting their hands in the school (which we donâ€™t recommend you do!).” [source]