Zebrafish aboard China's space station are doing well in orbit, according to an update on the experiments.
The four zebrafish arrived at the Tiangong space station aboard the Shenzhou 18 spacecraft on April 26, along with astronauts Ye Guangfu, Li Cong and Li Guangsu.
The fish live in a tank that forms a miniaturized self-sustaining ecosystem. It uses a plant called hornwort, which carries out photosynthesis, to sustain the lives of the fish, according to state broadcaster China Central Television (CCTV).
Scientists designed the experiment to study how the space environment affects their growth and the overall system balance. Earlier, the fish had been observed doing strange things due to microgravity, such as unusual directional behavior and inverted swimming.
Related: Just keep swimming! Zebrafish doing fine in zero gravity on China's Tiangong space station (video)
The scientists have expressed hope that the fish may lay eggs. If they do, the Tiangong astronauts will be able to closely follow the development of any offspring, as zebrafish embryos are transparent and develop outside of the uterus. If this happens, it would not be the first case of fish bred in space, as medaka fish mated on a 1994 space shuttle mission.
"In space, we conducted the country's first in-orbit aquatic ecological research project — that is, raising fish in space," said Li Guangsu. "We observed the zebrafish growth in the space station, which have accompanied us for several months. As the mission requires, we have to carry out over 90 experiments and tests, and all of them are progressing smoothly."
The experiment is China's first in-orbit aquatic ecological research project. It is being carried out in cooperation between the Institute of Hydrobiology and the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences.
The project aims to make a breakthrough in the cultivation of vertebrates in space, according to CCTV. The experiment may shed light on the challenges of maintaining life support systems for long-duration space missions.
Meanwhile, the three Shenzhou 18 astronauts could be back on Earth within the month, as their six-month-long orbital mission draws to a close. China's human spaceflight agency has, however, yet to release a date for the launch of the new Shenzhou 19 mission and subsequent return of Shenzhou 18.
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