In 1998, scientists sent 4 pregnant swordtail fish and 200 babies into space; near the end of the mission, the fish suddenly began swimming in continuous loops

In January 1998, four pregnant swordtail fish and 200 of their young left for space on the space shuttle Endeavor. They traveled inside a sealed aquatic module built to house them for the mission. According to NASA records, Endeavor launched from Kennedy Space Center, Fla., on Jan. 22, 1998, to test the effects of space travel on various forms of life. The fish swam as they always had for most of the journey. Then, near the end of the voyage, their motions took a turn that researchers were not prepared for.

Four pregnant fish became unlikely space travelers