The usual explanation for flight in flying fish is as a way to escape predation, particularly from fast-swimming dolphin-fish.
Flying fish do not fly to catch insects, flying fish are largely oceanic and flying insects are rare over the open sea.
It has been suggested that their flights, which are actually glides, because flying fish do not flap their “wings”, are energy-saving, but this is very unlikely as the vigorous takeoffs are produced by white, anaerobic muscle beating the tail at a rate of 50 to 70 beats per second, and this must be very expensive in terms of energy use.
Flying fish have corneas with flat facets, so they can see in both air and water.
There is some evidence to suggest that they can choose landing sites. This might allow them to fly from food-poor to food-rich areas, but convincing evidence of this is lacking.
There seems to be little doubt that escape from predators is the major purpose of their flight, and this is why so many fly away from ships and boats, which they perceive to be threatening.
Strictly speaking, the flying fish does not fly, it indulges in a form of powered gliding, using its tail fins to propel it clear of the water.
It sustains its leap with high-speed flapping of its oversized pectoral fins for distances of up to 100 metres. The sole purpose of this activity seems to be to escape predators.
If one can manage to tear one’s eyes away from the magic of the unexpected and iridescent appearance of a flying fish, a somewhat more substantial fish can often be seen following its flight path just below the surface.
We have seen whole schools of flying fish become airborne as they try to escape tuna which are hunting them, and minutes later have seen the school of tuna attempt similar aerobatics as dolphins move in for their supper of tuna steaks.
A morning stroll around the decks of an ocean-going yacht will often provide a frying-pan full of flying fish for breakfast.
Presumably they are instinctively trying to leap over a predator, in this case the boat, but as they don’t seem to be able to see too well at night they land on the deck. They rarely land on board during the day.
Most alarmingly they will land in the cockpit, and even hit the stargazing helmsman on the side of the head.