Flying fish don't flap — they build speed underwater, then glide on stiff fins

Flying fish escape predators by swimming toward the surface at speeds up to 37 mph, then spreading enlarged, wing-like pectoral fins and breaking into the air. Once airborne they don't flap; they glide, using rapid tail vibrations against the water's surface for extra thrust if needed, covering distances over 600 feet in a single glide. More than 60 known species have independently evolved this trick.

— John Davenport, How and Why Do Flying Fish Fly? — Reviews in Fish Biology and Fisheries, 1994