1 Fish mated and laid eggs in space

As one of the space biology experiments for the second 
International Microgravity Laboratory (IML-2/ STS-65) 
mission carried out in the summer of 1994, four of a 
small Japanese killifish (Medaka, Oryzias latipes) made
 a space travel of 15 days. These four Medaka fish 
performed their successful mating behavior in space for 
the first time among vertebrate animals. Moreover, the 
eggs laid developed normally till hatching fry (baby 
fish) in space.
1. Medaka

  This IML-2 experiment was titled 'Mating 
Behavior of The Fish Medaka and Development 
of Their Eggs in Space.' The code name 
'MEDAKA' was given to this fish experiment 
in the mission. It is the Japanese name for 
this small fresh-water fish, which live all 
over the Japanese countryside (Latin name, 
Oryzias latipes) . We, Japanese enjoyed play
-ing with this fish in our childhood very much.
 This experiment aimed to study whether the 
fish Medaka can carry out mating and lay eggs
in space, and when eggs are laid, to observe 
their developmet of embryos. The IML-2 Medaka 
experiment accomplished its objectives to the 
point of 100 %, with quite a success: The fish 
mated, laid eggs in space, and these eggs 
developed normally to hatching (coming out as 
a baby fish) under microgravity.
  Listed below are several characteristics of 
this small killifish, Medaka. Only those 
necessary for understanding this IML-2 Medaka 
experiment are listed. 

Medaka ( a small killifish)
Classification      fish (teleost),   Oryzias latipes
Adult fish            0.7 g in weight,  3 cm in length
            Female and Male are different in the shape of 
                 Dorsal fin and Anal fin 
Conditions for mating and laying eggs
            Light                  14-h light / 10-h dark
            Temperature       23 - 28  
Mating habit
            Once started laying eggs, fish mate
                 and lay eggs everyday.
            Each day, within 2 hours after the light gets on, 
                 fish mate and lay eggs.
Eggs and Embryos
            Egg size           1.0 mm (diameter)
            Number of eggs     ca. 5 - 25 eggs /female/ day
            Hatching           ca. 10 days after fertilization  
                                                    (at 24 )



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