Fight-or-flight is a general response that all organisms in an ecosystem must act upon during their life when their survival is threatened, even for some marine species the flight part is literal. Amazingly, the laws of physics and aerodynamics have allowed for a family of marine fish called the Exocoetidae to evolve to be able to fly and glide close to the surface of the water. These unique beings are also more commonly known as flying fish and there are about 40 known species. Scientists believe that modern flying fish evolved independently about 66 million years ago, even though the oldest known fossil of a flying fish was 235-242 million years old. They are thought to have evolved from half-beak-like ancestors that had a long tail allowing them to swim fast in the high drag zone near the surface. Flying fish are generally very small but some can grow up to be about 45 cm long, bearing in mind that most of them are far smaller than that. They can be found in all of the oceans, but more abundantly in warm subtropical and tropical waters. The uncommon ability of flight in fish is a natural defense mechanism to avoid predators, as the flying fish are non-predatory and mostly eat plankton and algae.

Figure 1. A flying fish gliding through the air, close to the surface of the Tasman sea. (source)
Figure 1. A flying fish gliding through the air, close to the surface of the Tasman sea. (source)

How take off happens

Contrary to general belief, flying fish do not flap their wings like birds to gain lift, instead they use the momentum of their acceleration to enter a free flight, which can be prolonged by taxiing with fully expanded lateral fins. The entire process of taking flight from water begins with the fish accelerating to reach a velocity of about 60 km/h underwater. It then angles upwards and breaks the water surface while taxiing with its tail still submerged. In order to get enough thrust and momentum to take flight, the tail of a flying fish beats underwater up to 50 beats per second, this allows the fish to rise up to the air, gliding long distances, up to 200 meters at once. If a flying fishes body is starting to near the water surface again, it can beat its tail underwater to taxi and to continue gliding without ever being fully submerged. With consecutive glides, a flying fish can travel great distances of up to 400 meters and as fast as 70 km/h, but most importantly it is safe during its flight from its usual marine predators, such as mackerel, tuna, squids etc. A challenge during flight is to avoid the predatory birds that prey on these small fish. The reason why these creatures are mostly only found in warm tropical and subtropical waters is because according to studies, it is unlikely that a flying fish would be able to fly in waters that are below 20 °C. The colder waters would fundamentally restrict and limit muscle function in the fish too much for it to be able to propel itself into flight.

  • Did you know? To put the impressive 60 km/h underwater top velocity of flying fish better into context; an average human can swim up to about 4-5 km/h and a great white sharks top velocity is around 55-60 km/h.

Morphological adaptations due to natural selection:

Natural selection is the underlying cause for such unique adaptations, and in this case the ability of flight is an adaptation to dramatically increase the success rate of escaping marine predators. The proof that flying fish have evolved to fly in order to escape their predators can be seen in their impressive specialized aerodynamic designs that have developed over time. Their pectoral and/or pelvic (depending on species) fins have evolved to be hypertrophied and they possess a cylindrical body with a ventrally flattened surface to reduce friction with the air and water. Some flying fish have two wings (pectoral) and some have got 4, meaning that both pectoral and pelvic fins are used in flight. The ones that have 4 wings have evolved their expanded pelvic fins to function as stabilizing factors behind the fish’s central point of gravity. So basically a flying fish with 4 wings doesn’t use its extra 2 pelvic fins for uplift. According to research, fin span and fin area increase with increasing body mass. The fins of flying fish are designed for high lift with low drag characteristics and a high speed glide. Due to natural selection, flying fish have evolved and grow to become optimized for gliding for long distances. They grow in a slightly negatively allometric way, meaning that they become thinner with increasing body length. Surprisingly, in terms of wing loading and morphology, flying fish resemble birds and bats more than other gliders as they narrow their wings when traveling at fast speeds in order to improve flight performance. The largest of flying fish on the other hand exhibit wing loading more similar to pelicans and cormorants. Wing loading has a positively allometric relationship with body length, because of the fact that they can’t increase relative wingspan during growth.

A flying fish during take off, propelling with its tail to generate enough speed and momentum. Taken in Isimangaliso Wetland Park on the North Coast of South Africa. (source)
Figure 2. A flying fish during take off, propelling with its tail to generate enough speed and momentum. Taken in Isimangaliso Wetland Park on the North Coast of South Africa. (source)

Did you know? Flying fish are attracted to light and fishermen use a luring light at night to capture them. The vessel will have enough water to sustain fish, but not enough to allow the flying fish to escape by propelling themselves out.

Research suggests that flying fish have evolved the ability to fly because of challenging environmental factors in its habitat, which is the epipelagic zone in the water column. This area of the water column, being as diverse in life as it is, does make it an extremely difficult environment for a small fish to survive in. Because of the diversity of the epipelagic zone, it contains numerous predators, meaning that the small flying fish must have undergone significant morphological and biological adaptations to allow it to thrive and survive in a dangerous and large ocean.

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