in your case your fish is your AI, this video series will show you how you can make an AI jump, you will need to do extra logics to make the fish jump ex: overlap character or something like this and play the animation of fish jump along with the logic that will make damage to the character and make the fish follow the character position in range … so the fish will not only jump but it will follow the character in limited range while jumping like targeting character and play with its velocities too to make it smooth…
hope it will help, cheers!