An unusual deep-sea fish is helping Cornell researchers think through a quieter way to move an underwater robot. Their new study describes how an oarfish can propel itself with ripples along its long dorsal fin while keeping much of its body still.
The Cornell Chronicle report says the research, published Sept. 30 in Ichthyology and Herpetology, examines the anatomy behind that motion. It is an anatomical study, not a demonstration that an oarfish-inspired robot has already been built or tested at sea.
Oarfish have hundreds of bony rays extending into a membrane along their backs. The researchers found that muscles, cartilage and a ball-and-socket joint allow each ray to rotate independently through a full circle. Coordinated movement sends waves through the membrane, generating thrust that can move the fish forward or backward.
The team used dissections, tissue analysis, X-rays of a Smithsonian specimen, CT scans at Cornell and video analysis to examine the fin system. Intact specimens are hard to obtain because the long fish tend to break into segments after death, Cornell said.
Unlike an eel, which moves much of its body from side to side to swim, an oarfish can use its fin to move with less lateral body motion. The system may help it approach small crustaceans quietly and hold a vertical position while feeding, according to the researchers.
Rob Shepherd, a Cornell mechanical engineer, began discussing the fish with retired ichthyologist Willy Bemis while considering a large, quiet ocean-monitoring robot. The proposed machine would carry instruments and move without alarming aquatic animals. Shepherd's work is supported by the Office of Naval Research; the release does not describe a completed machine or report measured noise reductions.
The study's lead author is Gabriel Afonso, now a doctoral student at the Virginia Institute of Marine Science, and Bemis is its senior author. The researchers say the fin structure also raises a broader question: whether other fish that swim with ribbon-like fins evolved the same rotating joints or found different mechanical solutions.
FingerLakes1.com is the region’s leading all-digital news publication. The company was founded in 1998 and has been keeping residents informed for more than two decades. Have a lead? Send it to news@fingerlakes1.com.