To play Fish IO: Be the King, use the joystick (on-screen for mobile or WASD keys for desktop) to move your shark and the mouse to aim. Attack rival fish from the sides with the left mouse button or tap to eliminate them, avoiding their blades to prevent defeat. Consume sushi scattered across the arena to gain energy and collect fish heads to boost your score. Choose your fish and weapon at the start to optimize speed, rush, or defense. Strategize by targeting weaker opponents and using power-ups like shields wisely. The game supports fullscreen mode and is playable on browsers or via the Fish IO app on iOS and Android devices.