Download Underwater Animals Pack FREE Unity. 

This package contains more than 100 different animal species of fish, mammals and more. It contains more than 100 different animal species of fish, mammals and more. The package contains more than 100 different animal species of fish, mammals and more.

Check out the details from the Unity Asset Store: https://assetstore.unity.com/packages/3d/characters/animals/underwater-animals-pack-2851