This was a fun relaxing lil game! I really like the art and atmosphere. I think there's potential in this idea.
Part of me wonders if you should have some kinda katamari demacy mechanics where as you eat fish your current fish gets bigger and bigger and can eventually eat fish that were previously too big.
Also, Is it possible to see the shark? I was playing for a bit and got all the upgrades but the shork never showed.
Cute lil game, nice job!