What is the colony of fish?

The collective noun for a group of fish is a shoal or a school.

* Shoal is used for a group of fish that are swimming together in a loose formation.

* School is used for a group of fish that are swimming together in a tightly organized formation, often moving as one unit.

While "colony" is often used for groups of insects, birds, or other animals, it is not typically used for fish.