Do flying fish really fly? No, flying fish don’t really fly, but they can glide through the air for some considerable distance.
Flying fish are sometimes known as flying cod, but they are not cod. When cooked, they are said to taste like cod, which could be where the nickname comes from. They are a distinct family of fish called Exocoetidae, which comes from the Greek “exo”, meaning outside, and “koitos”, meaning resting place. Together, it means “fish that sleeps on the shore” and was given to the fish because people used to believe that they jumped out of the water to sleep on the shore. They don’t, and, just like most other fish, they can’t survive more than a few minutes out of the water. There are 64 different species of flying fish, and they are spread all over the globe in tropical and warm oceans.
In the same way that the flying squirrel doesn’t fly, flying fish don’t fly either. They have both developed adaptations that allow them to glide for long distances. Something like this could be the evolutionary start of being able to fly, and presumably, animals like bats started off by gliding before a mutation turned gliding into flying. In a million years, maybe flying fish and flying squirrels will actually fly, but today, they just glide.
Flying fish have fins that have evolved to be much wider and longer than the fins on other fish. These are their wings. They are curved in the same way that a bird’s wing is and produce lift in the same way. The part of their vertebrae where the fins connect has become wider as well, so that there is more space to connect the fins, which makes a very strong connection and allows the wings to be stable in flight and to support the weight of the fish. Their vertebrae are also adapted so that there is much more rigidity between the head and the whole spine to keep the fish as straight as possible when it is flying. Any curve or movement in flight would reduce its aerodynamic profile and cause it to come down more quickly. Some flying fish only have wings at the front, but some flying fish have two sets of wings, one at the front and one at the back. These flying fish can glide much further.
The fish usually swim just below the surface, but they can go down as far as 200 m. To take off, they fold their wings back along their sides to reduce drag in the water and shoot to the surface. They have so much speed when they hit the surface that they pop out, and they immediately straighten their bodies and unfurl their wings. They get enough lift to glide for about fifty meters before reentering the sea. Flying fish with four wings instead of two can glide much further, and the furthest observed distance by a flying fish was 400 meters. It is very difficult to test and observe them, so presumably some fish have gone further. Flying fish can reach speeds of about 60 km/h when they start their glide. They get this speed by swimming straight at the surface, and their powerful tail muscles and streamlined bodies push them extremely quickly. Dolphins use this technique as well, which is how they can jump so far out of the water. With the right conditions, flying fish can use the air coming over the waves in the sea to get even more lift and travel even further. They can use convection currents in the same way some birds do.
The most likely reason why they have evolved to fly is to escape predators. They are eaten by dolphins, squid, tuna, and other sea life, and being able to fly out of the sea and reenter it 400 meters away is a great method of getting away from a predator. However, it does make them targets for birds, which swoop down and pluck them out of the sky. Presumably, overall, there is more advantage in being able to avoid predators in the sea than in avoiding being eaten by birds, which is why this ability evolved. They also don’t fly very high, and their coloring makes them pretty difficult to spot, so they are not easy food for birds. They also have to account for the energy it takes to reach the speed required to leap out of the water. Although once they are flying, they don’t have wings to flap, and gliding requires no extra energy. It is said that they have the glide profile of some birds of prey, which can glide for hours. And this is what I learned today.
Sources
https://www.discoverwildlife.com/animal-facts/fish/flying-fish-facts
https://en.wikipedia.org/wiki/Flying_fish
https://en.wikipedia.org/wiki/Exocoetoidea
https://en.wikipedia.org/wiki/Flying_squirrel
https://www.iflscience.com/do-flying-fish-really-fly-65706
Image By http://www.moc.noaa.gov/mt/las/photos2.htm, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4084641