Can fish populate space? In 1994, four medaka fish were flown aboard Columbia. They laid 43 eggs; 8 babies were born in space with no gravity. Adult fish, however, forgot to use one organ in their body

Fish can survive and procreate anywhere, even in space. In 1994, space scientists had a pleasant surprise when they discovered that baby fish and salamanders generated eggs at breakneck speed aboard the space shuttle Columbia. Four mendaka fish were carried into space in the early 90s to test whether fish could reproduce in microgravity.

The experiment was conducted on board the Space Shuttle Columbia, or STS-65, as part of the Second International Microgravity Laboratory (IML-2) mission. Together with Japanese astronaut Chiaki Mukai, the four medaka spent fifteen days in space.

The experiment was suggested by Dr. Ken-ichi Ijiri, an associate professor at the University of Tokyo at the time, according to the Japan Aerospace Exploration Agency (JAXA). During the experiment, 43 eggs were identified by the researchers. Fish were the first known vertebrates to deposit eggs in space. More significantly, eight of the eggs hatched while the fish were still in orbit, and the eggs matured normally. Later on, the baby fish were dubbed "space medaka".

How Did Scientists Prepare the Fish for the Mission?

Fish rely on their bodies and internal organs to control their balance in the water. In microgravity, they could start to spin uncontrollably, as they do not have Earth’s gravitational pull anymore.

Scientists tried many medaka on parabolic flights prior to the trip. During these flights, an aeroplane takes a unique up-and-down trajectory that produces microgravity for roughly 20 seconds at a time. This allowed scientists a brief window of time to see how the fish behaved in the absence of regular gravity.

After many experiments, the scientists were able to select a species of fish that would be able to survive and not lose balance in microgravity. They had better eyesight and were better at using their vision to control their position, rather than being overly dependent on their otoliths (organs that help fish maintain balance). Four fish were selected and named Cosmo, Genki, Yume, and Miki. The fish tank was maintained at a water temperature of 24 degrees centigrade.

Additionally, the fish adhered to a 14-hour light and 10-hour dark cycle. The medaka often spawned in the morning; therefore, the lighting schedule was crucial. They kept laying eggs once a morning during the expedition, usually two hours after the lights came on.

The fish were fed every three days. After gathering the eggs, the researchers were able to watch how they developed without the adult fish consuming them. The eggs were kept away from the adult medaka by water currents that carried them to a different area of the tank.

Fish’s Behaviour When They Were Back On Earth Baffled The Team

Although they survived, the fish started to sink when they were back on Earth. Moreover, they appeared to have forgotten how to use their swim bladders (an organ that helps fish maintain their position in the water). They also used their pectoral fins rather than tail fins to swim in the water while in space.

After returning to Earth, the baby fish that had hatched in space acted differently from the adults. Under the gravity of Earth, they were able to swim normally. After the mission, the fry also kept growing. They eventually numbered around 1,300 fish. The parents' time in space had no discernible consequences on the children, according to the research.