14. Jun, 2020

Fish that leap and fish that fly.

Several species of fish have the habit of making occasional leaps out of the water, which is also known as breaching. They may do so for different reasons. The leap could be part of their natural locomotion:  for example to save energy or just for fun like with the bottlenose dolphin. Spinner dolphins seem to enjoy their ability to spin multiple times in one jump. A jump could also reflect an attempt to catch a prey on the surface. A seal swimming on the surface may trigger a breach of the great white shark, and a fly above the surface of a river could tempt a trout to leap out of the water to snatch it. Other breaches reflect an attempt to escape a predator or noise of a boat propeller leading, for example,  to mass jumping of Asian carps in the  USA. These carps multiplied spectacularly after they escaped from a fish farm, outnumbering the local fish species. One fish jumping can set off a chain reaction and spook other fish — as seen in footage a river full jumping Asian carps in the Illinois River.  Spectacular are the jumps of salmons heading upstream to spawn that can leap up more than three meters to scale a waterfall. Some bony fishes such as mudskippers  (Periopthalmus) and amphibious blennies (Alticus) may spend more than 50% of their lives out of water. Anatomical (body) and behavioral adaptations let them move better on land and water. When threatened, these species typically produce prone jumps, using their fins to move around in skips. They may even flip their strong body to jump up to 2 feet (60 cm) into the air.

Sofar some examples of the leaping fish, but the flying fish are the ‘real’ flyers. They belong to the family Exocoetidae in the bony fish order of  Atheriniformes and closely related to the needlefish, halfbeaks, and sauries. Flying fish are limited to surface waters warmer than 20–23 °C, and contain about 64 species,  grouped in seven to nine genera. While they cannot fly in the same way a bird does, flying fish can make powerful, self-propelled leaps out of the water where their long wing-like fins enable gliding for considerable distances above the water's surface. Spotting a group of flying fish is a bit like seeing jumping dolphins. It is always fun to see a group turning up next to your boat and then performing its extended flight over the surface. In the open Oceans, flying fish are sometimes ending up on the decks of sailing boats or on larger cargo ships when the weather is rough. There are also stories of castaways surviving by eating flying fish that fell on their boat and swearing afterward never to eat sashimi for a long time.

Flying fish mainly fly to escape from predators, particularly dolphin-fishes (Coryphaena hippurus). Adult flying fish are of variable size (150–500 mm maximum length) and may be broadly divided into two categories: ‘two-wingers’ (e.g. Fodiator, Exocoetus, Parexocoetus) in which the enlarged pectoral fins make up most of the lifting surfaces, and ‘four-wingers’ (e.g.Cypsilurus, Hirundichthys) in which both pectoral and pelvic fins are hypertrophied. The pectoral fins are controlled by two groups of muscles, the lateral muscles that extend the wings, and the medial muscles that furl them. Both groups appear from external appearances to be red (aerobic) muscles (see the  Springer article for more details)

Beyond their useful pectoral fins, all have unevenly forked tails, with the lower lobe longer than the upper lobe. When the lower lobe touches a flat water surface it often draws a sinusoidal track. The process of taking flight, or gliding, begins by gaining great velocity underwater. After it has jumped out of the water produced by the rapid movement and vibration of the tail, they use their large pectoral fins almost as wings.  The pectoral fins then expand and stiffen like the wigs of a glider while in the air before the fish reenters the water. A flying fish can remain airborne for at least 40 seconds and can reach a top speed of at least 40 MPH (64 km/h). With a good wind however they might even fly as far as hundreds of meters.  When gliding, flying fish barely skim over the surface of the water. When the fish returns in the water it may become airborne again by violent flapping and extra thrust of its forked tail. As said, their flying action is meant to escape from predators (such as fish-eating bonitos, albacores, dorados, or the dolphin fish).  A Zodiac running across a group flying fish swimming close to the surface may also provoke a jump out of the water, as I witnessed several times on the Mediterranean.  In some Oceans airborne flying fish are confronted with another danger from the sky above: seagulls and frigatebirds looking for a tasty snack. Here they are literally caught between the ‘devil and  the deep blue sea