It lives hidden in the depths of the ocean, and its way of swimming inspires aquatic robotics

A oarfish swims with its body almost straight while its long dorsal fin undulates continuously A team from Cornell University observed that the oarfish (Regalecus spp.) can move forward and backward without bending its elongated body. The research analyzed the dorsal fin of this marine animal that is rarely seen. Interest in the mechanism also arose from engineering. Rob Shepherd, director of Cornell's Organic Robotics Lab, was working with the United States Office of Naval Research on the design of a large, silent aquatic robot. The goal was to create a machine that could transport instruments intended to monitor the state of the ocean without scaring fish or other animals. According to Earth.com, that robot could swim in both directions with a system inspired by the oarfish's fin. The work, published in the scientific journal Ichthyology & Herpetology, identified that the hundreds of rays—rigid, bone-like structures that support the fin—can rotate independently and completely. The scientific journal Ichthyology & Herpetology published the study on the oarfish's propulsion mechanism (Courtesy, study: Musculoskeletal system of the dorsal fin of oarfishes (Regalecidae): fin rays as rotary elements in an undulatory system, published in Ichthyology & Herpetology) This movement produces waves along the dorsal tissue, allowing the fish to control its trajectory without resorting to the lateral undulations typical of other long-bodied species. Biologists call the structure located on the back of fish the dorsal fin. In the oarfish, it consists of a thin layer of tissue supported by numerous rays, capable of moving thanks to a joint located at their base. Each fin ray connects to muscles and cartilage through a joint that allows it to rotate in different directions, like a ball in a socket. This configuration allows it to complete a 360-degree rotation, a range that researchers compared to the operation of a mechanical control lever. "They use the dorsal fin to propel themselves without moving the body laterally," explained Willy Bemis, a retired Cornell biologist and one of the authors. The specialist noted that oarfish also undulate their bodies, though they have this second method of locomotion. A team from Cornell University discovered that the oarfish can move forward and backward without bending its body (Courtesy, study: Musculoskeletal system of the dorsal fin of oarfishes (Regalecidae): fin rays as rotary elements in an undulatory system, published in Ichthyology & Herpetology) When the rigid structures are activated one after another, they generate waves that travel along the fin and push the animal through the water. In this way, the fish can move forward or backward while keeping the rest of its body straight. The peculiarity is that the waves do not all have to travel in the same direction. One section of the fin can send movements toward the tail, while another directs them toward the head; that combination gives it more precise control of its position. "They are able to continuously change the pattern of the dorsal fin rays, and they do it very quickly," Bemis said. "The fin rays are incredibly mobile," the researcher added, describing a mechanism that allows thrust to be modified along the entire structure. The analysis of one specimen revealed the existence of 401 functional units distributed along its back. Each one includes a rigid structure, its supports, and the corresponding muscles, so it can act separately within the fin. The dorsal fin rays of the oarfish have joints that allow them to rotate 360 degrees like a control lever (Courtesy, study: Musculoskeletal system of the dorsal fin of oarfishes (Regalecidae): fin rays as rotary elements in an undulatory system, published in Ichthyology & Herpetology) Oarfish are large animals that rarely appear before people. Moreover, they are difficult to study after death because their bodies tend to fragment, a condition that limited the availability of samples for the scientific community. The research did not conduct experiments with live specimens. The team examined preserved specimens, thin tissue sections observed under a microscope, X-rays of a specimen preserved at the Smithsonian Institution, and CT scans performed at Cornell. Gabriel Vinícius Felix Afonso, of Cornell University's Museum of Vertebrates, led the work. The scientists also analyzed recordings of the fin's movement to relate the anatomy of the rays to the way they move through the water. The dorsal fin generates waves in opposite directions simultaneously to achieve precise movement control (Illustrative image Infobae) Unlike other species in the same order, the rays of this species are smooth pieces, without branches or joints along their length. Two bones support them, one on each side, while 3 pairs of muscles participate in their movements. Other aquatic organisms employ a similar method. Knifefish, for example, produce waves in a long fin located on the underside of their body. Previous research on those species sparked interest in reproducing ribbon-shaped fins in mechanical devices. The authors indicated that the individual's rotating joints could provide ideas for future underwater robots. However, it is still not known how a live specimen decides which pattern to activate in each ray while swimming.