Biological hydraulic system discovered in tuna fins

Cutting through the ocean like a jet through the sky, giant bluefin tuna are built for performance, endurance and speed. Just as the fastest planes have carefully positioned wings and tail flaps to ensure precision maneuverability and fuel economy, bluefin tuna need the utmost control over their propulsive and stabilizing structures as they speed through the ocean. The outstanding maneuverability and precision locomotion of these powerful fish are supported by a vascular specialization that is unique among vertebrates, according to new research from Stanford University and the Monterey Bay Aquarium: pressurized hydraulic fin control.

Through studying the anatomy, physiology, locomotion and fin movements of Pacific bluefin and yellowfin tuna swimming in tanks, researchers have found evidence of a biological hydraulic system in the large sickle-shaped fins centered above and below the tuna's body, called the median fins.

"Animals are exciting sources of elegant engineering solutions in aero- and hydrodynamics. What we have discovered in these tunas is unlike other animal hydraulic systems. It's a musculo-vascular complex that is integrating the lymphatic system, the skeletal muscles and fin bones," said Vadim Pavlov, a postdoctoral fellow at Stanford and a lead author of the research, published in the July 21 issue of Science. "We've shown that in tunas and their fast-swimming relatives this complex functions to generate hydraulic pressure that provides fine adjustment of the shape of their fins. By expanding or retracting their dorsal and anal fins, they alter the physical forces generated by fins, allowing for maneuverability."

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