A bait ball, or baitball, occurs when small fish swarm in a tightly packed spherical formation about a common centre. It is a last-ditch defensive measure adopted by small schooling fish when they are threatened by predators.
There are many kinds of Triggerfish. This is a Clown Triggerfish. They are very feisty and will bite your hand when trying to feed them. If you keep them in an aquarium they will bite tubes and stuff and cause real havoc! They have personality.