Each level of the game allows the player to unlock three new fish. One of them, the third fish, is always the most interesting and fun; however, it's also the most challenging to unlock. Here are three tips to help you catch the third fish every time:
Maximize your score: a high score will make the game spawn the next version of fish, and for this reason players should always keep an eye on the score, which is located at the top right corner of the screen.
Keep the water low: since the game ends when the water hits the top, keeping the water level low for as long as possible is a good thing. Popping the electric or tornado bubbles will increase the score without changing the water level. On the other hand, if you see a sponge, try to keep it above the water line as long as possible. It will grow after every turn and when it finally touches the water, will decrease the water level significantly.
Go for the combos: the best way to get a high score is to earn combos, which happens when multiple bubbles get popped at once. Also, note that none of the bubbles produce water drops, thus keeping the water level unchanged. Combos will definitely help get to the third fish!