Exploring the unique swimming dynamics of seahorses

Of all the creatures in the sea, perhaps the strangest swimmer is the seahorse. It is the only fish that swims with an upright posture, giving it a unique appearance and hydrodynamic characteristics. However, very little research has gone into investigating how seahorses swim.

Li et al. developed a 3D model of a seahorse and conducted numerical simulations to study its swimming characteristics. They introduced a self-propulsion method and studied the resulting dynamics.

The seahorse employs a unique propulsion method using the large dorsal fin on its back. This fin engages in two simultaneous movements: a sinusoidal back-and-forth motion, and an undulating motion from top to bottom. This combination produces both a forward and upward force, although not of equal magnitudes.

“Because the traveling wave generated by the seahorse’s dorsal fin propagates from top to bottom while swimming upright, the vertical force is greater, and the horizontal thrust along the swimming direction is smaller,” said author Xiaohu Li. “This leads to a slow forward speed and low swimming efficiency.”

The researchers plan to conduct more simulations to better understand the mechanics underlying upright swimming. They hope their work can be used to give people working underwater a more familiar orientation.

“Humans are used to walking upright on land, but when in the water, they need to swim in a horizontal posture, which is inconsistent with the human habit of standing on two feet,” said Li. “If people can swim upright in the water like seahorses, then they may unleash the potential of their hands and thus improve the efficiency of underwater operations.”

Source: “Hydrodynamic analysis of the upright swimming of seahorse,” by Xiaohu Li, Gong Chen, Yanbing Tang, and Jisong Zhong, Physics of Fluids (2024). The article can be accessed at https://doi.org/10.1063/5.0187694 .