Technologies and Analyses Using Medaka to Evaluate Effects of Space on Health

Operation of the International Space Station (ISS) has begun. It is important for astronauts to stay healthy and comfortable in space. Reducing influences of environmental stress on astronauts during space flight is a subject of space medicine. With this background, we at the Japan Aerospace Exploration Agency (JAXA) Space Biomedical Research Office (J-SBRO) conduct research to understand and address the effects of the space environment on human health.Although the abovementioned research is of great importance to human health, it is often very difficult to verify by clinical research alone. Especially the effect of radiation is one issue becoming increasingly important due to the continuous accumulation of space radiation during long-duration stays in space. With their ease of breeding and transparent development, small teleosts are good model organisms. Medaka, the vertebrate, is an ideal model for space medicine. We are using medaka, which have a wider range of the habitat conditions, such as breeding temperature, than zebrafish, and have a history in radiation research, to verify the effects of the space environment. In this review, we are going to introduce medaka experiments at a cellular, tissue, and individual level for space medicine.