Natures wonders: tuna fin hydraulic controls (Introduction)

by David Turell , Thursday, July 20, 2017, 20:50 (2681 days ago) @ David Turell

Tuna can change fin shape by lymphatic fluid pumping:

https://phys.org/news/2017-07-biological-hydraulic-tuna-fins.html

"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.

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"'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."

"The tuna's ability to move these median fins quickly and precisely with a hydrodynamic mechanism may be an advantage in turning maneuvers undertaken during prey search, feeding and long-distance swimming, where careful energy expenditure is vital.

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"The finding was unexpected. Pavlov found this sinus area in the fin and associated structures and invited me to see if it was associated with the lymphatic system," said Benyamin Rosental, a postdoctoral research fellow in stem cell biology and regenerative medicine and a co-lead author of the paper. "I think we realized pretty early that this is a novel finding and a unique system."

"To identify the origin of the vascular input into the hydraulic system and its connection to the lymphatic system, the team took a multidisciplinary approach. The researchers recorded videos of Pacific bluefin and yellowfin tuna swimming in the facilities at the TRCC where close proximity to the fish enabled them to see the subtle changes in angle of attack of the median fins. The footage allowed the researchers to establish how the tuna changed the area and shape of these fins in order to execute different maneuvers. Paired with computer model simulations, the team also showed how fluid flowed across the tuna, impacting the forces generated by the fin at different swimming speeds.

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"Lymphatic vessels are normally small and difficult to distinguish by the naked eye, but in tuna they are transformed into a specialized system of large vessels and channels in median fins. With lymph acting as hydraulic fluid, increased pressure in these channels affects the fin's position and, probably, the stiffness that together alters hydrodynamic properties of fins. The capacity to rapidly adjust the fin positions affects the lift to drag forces on the fins and prevents the tuna from rolling and yawing during active swimming, limiting energy loss during long migrations.

"Tuna have numerous morphological, physiological and behavioral adaptations to move rapidly through the water column and a sophisticated physiology that includes elevated metabolism, a unique cardiovascular system and a warm body temperature. These features require a well-developed lymphatic system to maintain water balance in tissues and protect organisms from infection. Now, the evolution of tuna physiology can also include this unique hydraulic function."

Comment: These are complex mechanisms that show obvious purpose in design. It is all throughout evolution