Why do flying fish leap out of water?

Answer: Escaping underwater predators

Playing and having fun — Wrong. Leaping is energy-expensive and risky, since birds can snatch them mid-air. It's escape behavior, not recreation.

Escaping underwater predators ✓ — Correct! When chased by tuna, dolphins, or swordfish, flying fish burst through the surface at over 55 kilometers per hour, spread their enlarged pectoral fins like wings, and glide up to 200 meters through the air. Their pursuers can't follow, and they even 'taxi' on their tail to extend each flight.

Breathing air like dolphins — Wrong. Flying fish have gills and breathe underwater. They leap to escape predators, not to breathe air.