For this boss battle:
1. Find one of the rafts with food on it and break the container.
2. While Crikey is going over to eat the food, quickly go into the water and find an oxygen tank (easily seen by the bubbles), and hit it so it rises to the surface.
3. Crikey will go chew on the oxygen tank: hit the oxygen tank with your Flamerang while it is in his mouth to do damage.
4. Rinse and repeat until you've defeated him.