Medaka fish had the honor to perform the first successful vertebrate mating in space

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Among all the vertebrate species, medaka (Oryzias latipes) became the first species who demonstrated mating behavior in space. Moreover, the eggs they laid developed normally and hatched as baby fish in space. For a long time it has been believed that when exposed to weightlessness or microgravity (micro-G), fish exhibit looping behavior. Using the 20 seconds of micro-G realized by a parabolic flight of an airplane, we have found strains of this species which do not loop at all under micro-G. Four adult fish of the strain resistant to micro-G were sent to space. Selection of the four fish was crucial in the success of the space medaka experiment. Based on a hypothesis presented for posture control of the fish, strongly eye-dependent fish were selected. Selection procedures and what were achieved in space are described in detail. Post-flight studies on the offspring are also introduced. So far, no effects could be detected on the offspring of the four medaka fish who made a 15-day space travel aboard the space shuttle Columbia.



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