You can choose to play one, or use the full 20. At the bottom of the screen you will find the regular controls. Here you can pay close attention to your total bet, bet line number and automatic rotation number (if applicable). There is also a gambling button; more about this later.
Great Blue can play with only 25 to 125 points per rotation. It's the portal for the game's 10,000 jackpot, but you need to include 10 icons on the adjacent activity line to declare it. For four whales, it is 2,500, three of them are 250, and two of them are worthy of 10.