Effects of prolonged weightlessness on the swimming pattern of fish aboard Skylab 3.

Two fingerling fish and 50 embryonated eggs of (Fundulus heteroclitus) were flown aboard Skylab 3 in a plastic bag aquarium. Videographic picutres were taken with the on-board color-TV camera on flight Days 3 and 22 and video tapes were made for later evaluation on the ground. When observed first after 3 d in orbital weightlessness, both fish swam in tight circles for a considerable fraction of the observed time resembling the "looping behavior" as observed in previous studies with goldfish in parabolic aircraft flight. The frequency of looping diminished slowly after the third day until normal swimming was prevalent. At flight Day 22, both fish swam normally with their backs turned toward the light source. Looping episodes could still be provoked at this time by gentle shaking of the bag aquarium. Of the fish eggs carried aboard, 96% hatched during the mission. The hatch fry displayed normal swimming behavior.