The final option is to activate all 3 guns and use a larger bet of 100 to 1000 per game. Once you have selected the gun of your choice, you will enter the underwater scene and you can start shooting fish to get paid.
You will find the gun around the screen and your own gun is always at the bottom of the screen. You can use the plus and minus buttons to change your bet within your bet range, and you can use the back arrow to return to the selection screen to change your range and number of guns.