Sex differentiation of the gonad of fry transplanted into the anterior chamber of the adult eye in the teleost, Oryzias latipes.

In order to examine whether or not sex differentiation in the medaka, Oryzias latipes, is modified by the physiological level of sex hormones in the adult fish, trunk regions containing the gonads of newly hatched fry were transplanted unilaterally into the anterior chamber of the eyes of adult fish. The grafts could be classified into two types according to the vascularization. One type of graft developed well; some of them protruded from the eyes of the host fish. In these grafts the connexion of the blood circulation between the graft and the host was detectable without exception. The other type of graft consisted of those specimens without vascularization. The grafts of this type did not grow in size; this condition seemed to be similar to the so-called in vivo culture in the anterior chamber of the eye in rodents. Most of these grafts, however, degenerated. Judging from the histology of the gonad in the graft, a genetic male graft in the eye of a fish developed into a testis, regardless of the sexuality of the host. This fact was confirmed by two series of experiments. The gonad of a genetic female fry developed into an ovary if the graft was transplanted into a female fish. On the other hand, the gonad of a genetic female graft transplanted into a male fish failed to develop into an ovary, but formed spermatogenetic cells in a gonad of an abnormal structure. Therefore, it is highly probable that the reversal of sex differentiation from genetic oogonia into spermatogenetic cells is accomplished by the physiological level of the sex hormones in male fish. On the contrary, the sex reversal of genetic males to females is not induced by the physiological level of female sex hormones.