Northwestern-led study uncovers why fish look downward when swimming


Photo courtesy of Northwestern Now

As part of the study, scientists visited seven shallow-river sites across India naturally inhabited by zebrafish.

Jacob Fulton and Maia Pandey

When Ellen DeGeneres recorded her lines for the role of Dory in 2003’s “Finding Nemo,” she had no idea her character’s most iconic quote — “just keep swimming” — would foreshadow recently published research from Northwestern. 

A University-led study, released Wednesday in collaboration with international researchers, confirmed that fish look downward when they swim as a method of stabilization. Currents, foliage and other marine life can all impact a fish’s sense of motion, but the unmoving riverbed serves as a point of reference. By using riverbeds to orient themselves, fish can process their swimming direction and speed more accurately. 

“It was recently discovered that fish respond to motion below them more strongly than motion above them,” McCormick Prof. Emma Alexander, who led the study, said in a news release. “We wanted to dig into that mystery and understand why.”

Because the study focused on zebrafish — a widely studied model organism — researchers traveled to seven sites across India naturally inhabited by zebrafish to collect video data on the species. While laboratories often house tanks of zebrafish, Alexander said the researchers visited the creatures’ native environment to better understand their development. 

By plunging a robotic arm equipped with a 360-degree camera into the water, the scientists collected data to model hypothetical scenarios with simulated fish, Alexander said. 

“It allowed us to put our eyes where the fish eyes would be, so it’s seeing what the fish see,” she said in the release. 

The scientists then combined the hypothetical scenarios with data measuring zebrafish responses to certain motion stimuli. By simulating these hypotheticals in a realistic environment, researchers confirmed the adaptive behavior. 

These findings may hold wider implications for designs of artificial vision systems and bio-inspired robots. 

“If you were making a fish-inspired robot and you just looked at its anatomy, you might think ‘the eyes are pointing sideways, so I’m going to point my cameras sideways,’” Alexander said. “But, it turns out that the eyes are pointing sideways because they are balancing several tasks … they look upward to hunt and downward to swim.”

Email: [email protected]

Twitter: @jacobnfulton

Email: [email protected] 

Twitter: @maiapandey

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