Such a great and addictive game. I found a problem. When you spawn way too much objects, the game starts to get slower, even if those objects are destroyed / no loger visible. I think you should check your garbage collection, or pooling your sprites beforehand. You have a max number fo fishes, so it should not be a problem to have them all created beforehand and just putting them into play. Same may apply for coins (which seem to cause the problem) and bubbles.
Anyway, great game!