Choose the correct collective noun from the options below and fill in the blanks.

An ____ of fish swam in harmony in the aquarium.

Shoal

The correct collective noun for a group of fish is "Shoal." OPTION 4

Explanation:

Orchestra and Ensemble refer to groups of musicians or performers.

Array is a general term for an orderly arrangement of things.

Shoal specifically refers to a large group of fish swimming together.

So, the correct sentence would be: "An shoal of fish swam in harmony in the aquarium."