In 1973, NASA sent two fish into space to test their swimming ability in zero gravity; they initially swam in loops but later used light as cue to move normally after 21 days

When NASA launched the Skylab 3 mission in July 1973, astronauts were not the only passengers being studied. The spacecraft also carried two small mummichog minnows and 50 fertilised eggs as part of an experiment into how living creatures maintain their sense of direction in weightlessness.

Scientists chose the fish because their vestibular system, which helps an animal maintain balance and orientation, has similarities to that of higher animals. The experiment aimed to see what happened when the fish lost the constant pull of gravity that normally helps them determine which way is up and which way is down.