Like true "flying fish," the ribbon halfbeak has large pectoral fins that it uses like wings to escape aquatic predators by flying through the air. Unlike them, however, it lacks a set of winglike pelvic fins, which add much-needed rear stability while in flight. So, how does it manage? According to Dr. Yoshinobu Inada from Japan's Tokai University, it all comes down to a twist.

Upon making detailed observations of ribbon halfbeaks, Inada realized that they rotate their rear bodies by 90 degrees while flying. This brings their broad dorsal and anal fins into a horizontal orientation, allowing them to serve as stabilizers not unlike the tail of an airplane.

He also noticed that they frequently lift that rear end so that it sits higher in the air than their front end. By 3D-printing a model halfbeak and subjecting it to wind tunnel tests, he determined that this posture reduces the effect of downwash (from the pectoral "wings") on the tail wings, thus improving lift and flight performance.

The model halfbeak used in wind tunnel tests

"Other related fish species are also able to jump and fly over the sea surface, but only halfbeak twist their bodies for flight," says Inada. "This is a really unique behaviour."

He additionally believes that this new understanding of their flight mechanism could inform the design of tandem wing airplanes – while they're generally more efficient in flight than regular aircraft, they're subject to the problem of downwash from the main wing interfering with the rear wing.

Source: Society for Experimental Biology

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