If your moose gets bitten it will be very difficult to remain alive unless you are very close to the shore. If you do get bit, it is better to retry.
Killing fish
Try to aim and throw fish into your antlers to kill them. You will then have fewer to be concerned about and can create combos for better scores.
Piranhas
Throw away as many fish as possible from all directions, but focus on the area where your moose is located. Quickly remove any piranha that get close. This is indicated when the stars begin to sparkle. Act quickly before you are bitten.