I survived with 8 fishes. I see you have a lot of work on coding. Great job. but dont forget graphics are the first reputation people get from your game. So you have to put more work on the graphics.
For example you can draw / download a new fish skin and make them an animation. Also the ocrean could be a moving background with bunch of fishes. Walls could grow moss on them and the finish line could be their home (coral ?).
Work more on the graphics Im sure you will get more rating !
Good luck on your Unity journey.