How flying fish fly, described in e! Science News 9 Sept 2010, and Journal of Experimental Biology (JEB) doi: 10.1242/jeb.050880 and ScienceShots, 10 Sept 2010.

Flying fish have been observed to leap out of the water and glide for distances of up to 400m (1,300ft) at speeds of 70km/h. Haecheon Choi and Hyungmin Park, two Korean engineers from Seoul National University have analysed the aerodynamics of flying fish and found they are exceptional fliers close to the water surface and can glide as well as birds, such as hawks, petrels and wood ducks.

Choi and Park used five similar sized fish that had been killed, dried and stuffed, in a series of wind tunnel experiments to determine the lift to drag ratios for the fish with their fins in different positions and at different distances from the surface. Lift to drag ratio is a measure of the horizontal distance travelled relative to the descent in height during a glide and indicates how good a flying object is at staying airborne. Flying fish did best when they flew close and parallel to the surface with their wing-like fins spread horizontally.

The researchers also used smoke to visualise the flow of air around the fishes’ bodies and found “the tandem arrangement of the large pectoral fin at the front and smaller pelvic fin at the back of the fish’s body accelerates the air flow towards the tail like a jet, increasing the fish’s lift-to-drag ratio further and improving its flying performance even more.”

During their research they also analysed the stability of the fish with its fins swept back in the swimming position. They found it was unstable, which is “exactly what you need for aquatic manoeuvrability.” They concluded: “So flying fish are superbly adapted for life in both environments” (i.e. air and water).

Editorial Comment: If the researchers substituted the word “designed” for “adapted” we would agree with them completely. To explain how a fish that can only swim can convert to one that can swim and fly you have to explain how the genetic changes came about for growth of the fins into the right shape, and also how the fish came to know to hold the fins in the right configuration for flying. Simply jumping out of the water, as many fish do, will not achieve this no matter how long they do it.

Evidence News 22 September 2010

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