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2 Post-flight experiment: Effects on offspring

When adult fish came back to the ground, their mating and laying eggs 
were checked everyday. Tracing of the development of the eggs laid was 
carried out everyday for a month or more. Such studies on their 
offspring gave us informations about the effects of microgravity on 
gametogenesis, i.e., sperm-forming process in testes of the space
-traveled adult males and egg-forming process in ovaries of the females. 
So far, no offspring effects have been detected for the space-traveled 
adult fish or space-originated fish.

1. Space Medaka and their offspring

   As reported above, the four adult fish seemed 
to have enjoyed 15 days space travel, well 
accomodated to microgravity (micro-G). They had 
a little trouble in swimming for 3 days after 
returned to the Earth (Fig.1), and on the 4th 
day could recall how to swim under 1 g conditions    
(Fig.2). Probably, it takes about 3 days for fish 
to reprogram his brain networks. Some astronauts 
also say they need 3 days to fully adapt to the 
gravity of the Earth, which may imply that in such 
responses there is not much difference in human 
and fish. They both are vertebrate, anyway. The 
adult fish re-started mating and laying eggs on 
the 7th day after landing and continued to do so 
everyday afterward (Fig.3). For forty days, we 
counted the number of eggs laid on each day and % 
of fertilized eggs, and traced their development 
to obtain % of hatched 

Fig.1 When returned from space, the fish had a hard time in swimming.

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