Good use of the theme! My only points of feedback would be:
-The scene feels a bit cramped, this could be the intention but it's not an environment in which the player can have a chance to build a big enough school (I never get more than 2 or 3, but I may just be noobing x3).
-Fish joining the school of fish could follow the player closer
-Remember to import pixel art without Billinear filtering!!! (Leave as Point, No filter)