Pacific bluefin tuna, delicious water monsters that can reach over 300 pounds and swim at speeds of up to 40 mph, have a natural hydraulic system built into their fins that allows them to slice through the ocean with speed and precision.
Tuna feeding at the Tuna Research and Conservation Center. Video: Stanford/YouTube. GIF: Jacob Dubé
In a new paper published Thursday in Science, a team of California researchers describes this hydraulic system, which they say is unique among vertebrates in its design. It could lead to the design of faster boats and autonomous vehicles that take some inspiration from the bluefin tuna.
According to this research, the hydraulic system of the Pacific bluefin tuna integrates its skeletal muscles, fin bones, and vessels—the biological equivalent of a mechanical hydraulic system's pumps, vessels, and actuators—to expand and retract the fish's fins. This allows for precise movements when they're swimming long distances or hunting for their next meal.
Barbara Block, a professor of biology at Stanford University, told Motherboard in an interview that tuna are known as stiff swimmers, and designed for long-distance travel, so you wouldn't initially expect them to be able to move so nimbly. "They're capable of catching prey that is quite small, like a sardine or a mackerel, who are highly mobile," she said.
Block and other researchers from Stanford and the Monterey Bay Aquarium observed this by watching the tuna's movements at the aquarium, and noticed an unusual cavity that filled with liquid on the fish's dorsal and anal median fins. "So really what you're looking at is a hydrodynamic mechanism that when you pressurize this cavity, it creates this change of shape to the fin, you're giving the animal a turning moment," Block said.
Biological hydraulics have been found in animals before, in invertebrates like jellyfish and mollusks, but it works differently in tuna. Block said that this is the first time a hydraulic system like this has been observed in vertebrates.
"A lot of what happens in the ocean is not transparent. We've got a lot of organisms, a lot of biodiversity, in which we barely understood their specialization," she said.
Learning more about how the Pacific bluefin tuna speeds through the water could improve the design of sailing ships, which are already inspired by the tuna's aerodynamic body shape.
"We've got a lot of vehicles being designed for the sea. Some even look like tuna, but it's interesting that we're just realizing that they're using this really advanced bio-hydraulics to change the lift surface that changes the turning," Block said. "That would be something that would be very easy to implement in both autonomous vehicles and sailing boats' air design."
It wouldn't be the first time technology has learned a thing or two from Mother Nature. To name just a couple examples, A German automation company created an octopus tentacle robot for gripping objects, and the flight methods of bats have been studied to create flying drones.
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