3:Sex in space: the 3rd day of the mission

Now, their sex life in space. Figure 6 summarizes all of their mating behaviors on the 3rd day in space. The ordinate shows the stage number in mating behavior as fully described above. The abscissa shows time after the beginning of a light-period of the day. Thus, a vertical bar indicates how far a fish couple went through in one attempt of mating. The fish couple is indicated, for example, as AC, meaning male fish A approached fish C and tried mating.
The 3rd day of the mission was the best day for male A. At 7 min after the light-on, to our surprise he exhibited a circle dance of courtship to another male B, who of course neglected such a behavior (Fig.6a). Then, male A approached female C without dancing and they went far to stage 3, however separated before reaching the final stage, loosing their posture-control in weightlessness. Soon female C was courted by another male B, ending only at stage 2. At 35 min, A and C starting at a circle dance (Fig.7), succeeded in going all through to the final stage, i.e., stage 4 which includes reaching an orgasm, shedding eggs, ejaculating sperm and fertilization of eggs. The actual criteria for stage 4 were the detection of eggs on the female belly, as shown with () when eggs were noted. Later, male A again danced in front of C, who had already mated with him and laid eggs showed no interest at all.
Shortly before this love, male A was also showing his dance to female D (Fig.6b). In his disgrace, at 32 min A embraced D in an odd fashion with his head and tail in the opposite direction to the normal style. In Fig.6, the () is placed when such a 'head-to-tail' style was observed. A typical mating in this style is shown in Fig.10a. Repeating mating behavior several times stopping either only at the dance (stage 1), embracing (stage 2) or shaking (stage 3), they could not go beyond until at 1 hr 19 min when the stage 4 was finally attained by this couple. From 1 hr 11 min embracing was performed at six different times, of which last time (1 hr 19 min) they managed to accomplish the fertilization (Fig.8).
On the Earth, the fish usually reach the final stage embracing once or in some instances twice, and never make such frequent failures. We checked these four fish had been continuously mating and laying eggs everyday until loading them into the shuttle. Therefore, they should have a good experience in mating on the ground. In space or in weightlessness, even a playboy A had a hard time to perform mating when he has to keep his posture and also hold the female in a right position.

[Chapter3]| 1.Eating in space
2.Mating behavior of Medaka fish
4.Sex in space: the 5th day of the mission
5.Love and hatred among the four fish
6.Maternal love
7.The first successful vertebrate mating


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