Robotic fish could perform underwater-recovery missions

The robot — developed after observing and creating computer simulations of the black ghost knifefish — could pave the way for robots that could perform underwater recovery operations or long-term monitoring of coral reefs.

The black ghost knifefish, which hunts for prey at night in rivers of the Amazon basin, uses a weak electric field around its entire body, moving both forwards and backwards using a ribbon-like fin on the underside of its body.

Malcolm MacIver, associate professor of mechanical and biomedical engineering at Northwestern’s McCormick School of Engineering and Applied Science, has studied the knifefish for years. Working with Neelesh Patankar, associate professor of mechanical engineering, he has created mechanical models of the fish in the hope of better understanding how the nervous system sends messages throughout the body to make it move.

Planning for the robot — called GhostBot — began when graduate student Oscar Curet observed a knifefish suddenly moving vertically in a tank in MacIver’s lab. Further observations revealed that while the fish only uses one travelling wave along the fin during horizontal motion (forward or backward depending on the direction on the wave), while moving vertically it uses two waves. One of these moves from head to tail, and the other moves tail to head. The two waves collide and stop at the centre of the fin.