Just an animation that would be better with water music.
I like the animated fish and the upward movement of the bubbles. The secret of the fish movements is that they can be programmed to look the same fish when upside down. The fish in the sprite library don’t do ‘upside down’. Here the children have to make use of the Scratch Paint Editor (or external graphic editor). I like to encourage the children to ‘push the walls out’ by creating their own sprites.