Everyone has seen fish swim in the water, and dead fish can swim against the current? It may sound a bit ridiculous, but the 2024 hilarious Nobel Prize in Physics was awarded to a study on the swimming of dead fish.
Scientists from the United States were honored for "demonstrating and explaining the swimming ability of dead trout." The study not only reported a surprising and magical phenomenon, but also revealed the mysteries of fluid dynamics, providing a new perspective on how fish use eddy currents in water to conserve energy.
Fish swimming "each with its own unique skills"
Fish swim in a variety of ways and are far more complex than we think, the most common being swing swimming, where the body of the fish curves in an S-shape, creating a traveling wave from head to tail that pushes the fish forward, but this is only the tip of the iceberg.
Some fish, such as sailfish and mackerel, swim cruise-style, and their bodies are streamlined with crescent-shaped tail fins, allowing them to swim at high speeds for long periods of time. In contrast, eels swim in a serpentine shape and produce large wavy movements throughout their bodies, making them suitable for navigating complex environments.
Interestingly, some fish have also developed special swimming styles that allow them to "walk" on the ocean floor with their pectoral fins, while flying fish can leap out of the water and glide over a distance with their pectoral fins, reflecting the adaptation of fish to different ecosystems.
Flying fish. Image source: Wikipedia
The fluid dynamics behind the stroke
To understand fish swimming, the principles of fluid dynamics are indispensable. When fish swim in the water, they are actually constantly manipulating the currents around them, and through the movement of their bodies and fins, they are able to generate and control eddies that gain propulsion.
Interestingly, the eddies created when fish swim are not random. Studies have found that fish that swim efficiently are able to produce an organized vortex system. These eddies not only provide propulsion, but also reduce the drag of the water, allowing the fish to swim faster and with less effort.
The energy efficiency of swimming in fish has been a focus of scientists, and studies have found that in addition to optimizing their body structure, fish also employ a variety of strategies to conserve energy. Some fish, such as tuna, are able to migrate thousands of kilometers over long distances, which requires extreme energy efficiency, and many also use "gliding" to save energy, which briefly stops after a few swings and uses inertia to glide for a distance. In addition, group swimming is also an energy-saving strategy, following the eddy generated by the fish in front, and the fish behind can save a lot of effort.
Next time you observe fish in the Aquarium or river, pay more attention to how they swim. You may find that behind the seemingly simple oscillation, there are subtle mysteries of fluid dynamics, and these mysteries are inspiring us to create smarter and more efficient future technologies.
Whirlpool Street Swimming: A unique way to swim
When a fluid flows through a blunt object such as a cylinder at a certain speed, the Karmen vortex is a series of eddies formed behind it in a regular alternating manner, presenting an orderly structure similar to that of a street. The research team was inspired by an interesting phenomenon: in rivers, fish often like to stay behind obstacles, and eddies and even whirlpools often appear behind obstacles. Scientists are curious whether fish can benefit from the special currents in these eddy areas. To explore this question, they devised an ingenious experiment.
Schematic diagram of Carmen Vortex Street. Image source: Wikipedia
In the experiment, the researchers placed a D-shaped cylinder in the sink to create a regular vortex. When live trout are placed in this environment, they exhibit a unique swimming style known as the "Carmen gait", in which the body swings in a large, low-frequency manner that surprisingly coincides with the frequency at which eddies are formed. This style of swimming seems to allow the fish to conserve energy while maintaining their position, or even swimming against the current.
United States National Aeronautics and Space Administration (NASA) photographing Carmen Vortex Street caused by a hurricane around the Juan · Fernández Islands off the coast of Chile. Image source: Wikipedia
But what really surprised me was that when the researchers experimented with dead trout, they found that even dead fish could exhibit a similar ability to "swim"!
Rainbow trout. Image source: Wikipedia
The mystery of the "resurrection" of the dead fish
So, how do dead fish "swim"? The answer lies in the principles of hydrodynamics and the soft properties of the fish body. When a dead fish is placed in a vortex, the water currents from different directions act on the fish body, causing it to swing periodically, and this passive oscillation happens to interact with the vortex in the current to produce a forward thrust.
The researchers found that the frequency and amplitude of swings in dead fish were very similar to those of live fish. This means that when fish swim with eddies, they are largely taking advantage of a passive mechanism. The softness and shape of the fish body have evolved over a long period of time and have become well-suited to this passive propulsion. In simple terms, this study reveals an ingenious way of using energy in nature. In turbulent currents, fish do not simply fight against the current, but learn to "go with the flow" and use the energy in the current to reduce their own energy consumption.
This research is not only interesting, but also has potential applications.
Understanding how fish use eddies efficiently, scientists can develop new underwater robot designs based on this. These robots may be more flexible and energy-efficient in turbulent waters, and understanding how fish use eddies may also help us design more efficient ships and submersibles. For example, the design of a ship's hull may consider how to make better use of the eddy currents it generates to reduce drag.
In addition, this study also provides a new perspective for us to understand the ecological behavior of fish. In rivers and oceans, the reasons why fish choose to stay or migrate in specific locations may be related to their use of the current's characteristics, which is important for both fish conservation and fisheries management.
The 2024 hilarious Nobel Prize in Physics may seem absurd, but it's actually instructive. It reminds us that there are surprises in scientific exploration, and that even a dead fish can reveal the mysteries of the natural world. This research not only deepens our understanding of fluid dynamics, but also shows how organisms skillfully adapt and use their environment.
The next time you observe fish in an Aquarium or river, pay more attention to how they swim and you'll find that behind the seemingly simple swing lies the subtle mysteries of fluid dynamics that are inspiring us to create smarter, more efficient future technologies.
bibliography
[1]James C. Liao, Neuromuscular Control of Trout Swimming in a Vortex Street: Implications for Energy Economy During the Kármán Gait
[2]David N. Beal et. al., Passive Propulsion in Vortex Wakes
Planning and production
Produced by丨Popular Science China
Author丨Wang Jiayin, Academy of Advanced Technology, Chinese Academy of Sciences
Producer丨China Science Expo
Editor-in-charge丨Dong Nana
Reviewer丨Xu Lai Linlin