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Fish Locomotion

Submitted by kheredia on Thu, 10/31/2019 - 10:49

A variety of mechanisms allow fish to propel themselves through an ever-changing environment. Locomotor techniques such as wave-like motions are currently being researched, and with the help of recent technological advances, can now be examined in greater detail. In this article, George V. Lauder of Harvard University observed how morphological differences in fish, and the basic commonalities of swimming has become better understood. He viewed new approaches in kinematics, hydromatics and robotic studies of undulatory fish.

Lauder emphasized that not all fish use their fins the same way, because variations in their body shape make them complex. Stingrays are a unique example of this. Their flexible bodies and expanded pectoral fins help increase amplitude and lift. A study Lauder reviewed about center of mass dynamics (COM) went further in detail. Scientists compared a bluegill, clown knifefish, and an eel during surge and sway-like undulatory motion. The results from this study revealed that sway increased as speed increased. Researchers also observed that sway displacement was largest in eels. Lauder expressed that this particular experiment on COM was vital for understanding how physique affects aquatic propulsion, especially because COM research is lacking. He also notes that fish are able to alter the surface area of their fins. This helps them maneuver through difficult areas. In addition to kinematics, Lauder discussed a shark study which implemented a new hydromatic strategy by using 3D reconstructions of bonnethead sharks.

The experiment tested whether shark skin denticles have an effect on performance. Scientists 3D printed two bonnethead sharks, with and without denticles. When placed under appropriate swimming conditions, they discovered that intact surface skin increased the shark’s speed by 12.3%. This suggested that denticles can reduce drag, therefore improving performance. Biomimetics are an alternative to studying animals like the sharks in this study, because it is both harmless and safe for all that are involved.

Consequently, this has lead scientists to widen their range of research with recent advances in fish robotics. These realistic representations help researchers learn more about fish dynamics in an interactive way. Scientists manipulate variables, and even expose mimetic fish to several different conditions, without the limitations that might occur using live fish. Lauder analyzed an experiment which focused on modifying robotic fin supports to determine which level of stiffness corresponded with maximum performance.

Based on the results, the scientists in this study confirmed that a complex relationship between stiffness and flapping existed. As it turned out, optimal stiffness is based on the frequency of flapping. Constantly altering the shape of their fins allows fish to relax or stiffen their flippers and yield maximum performance with many different speeds. Despite the benefits, Lauder noted that physical models are still imitations and do not yet fully replicate the animals they represent. Even so, employing robotics in research is a safe and favorable alternative for animals that might be harmed for the sake of research. Evidently, these new techniques are incredibly helpful for understanding fish biology and provide innumerable opportunities for future research.