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Video: Fish Feel Their Way Around Obstacles

If you've ever stumbled back late at night to your dim apartment, where you tripped over a houseplant as you groped for the light switch, bluegill sunfish feel your pain. The freshwater swimmers (Lepomis macrochirus), notable for their flat bodies and yellow, orange, or red bellies, have to deal with numerous rocks and vegetation that block their path in the lakes and streams they call home. So how do they avoid accidents? They use their eyes, of course, but new research reveals that they also grope around like humans do. Scientists placed individual bluegills in separate tanks and had them swim through an obstacle course of acrylic tubes (video above). In order to ensure that the fish could rely only on their fins, the team turned out the lights or numbed the animals' lateral line nervous system, which allows them to sense shifting water pressure and motion (another method they use to find their way around). In each case, the fish tapped the tubes with their pectoral fins as they approached, using the feedback to successfully navigate the course. The finding, researchers report today in The Journal of Experimental Biology, could improve the design of robotic fish and other mechanical creatures.