SEXUAL DIFFERENTIATION IN THE TELEOST FISH XIPHOPHORUS HELLERII, AS MODIFIED BY EXPERIMENTAL TREATMENT

¹ Department of Zoology, Ohio University, Athens, Ohio

1. The normal sexual development and differentiation of Xiphophorus hellerii have been observed in the light of the adult sex ratio and the differentiation of the gonads from birth to maturity. The sexual differentiation has been shown to follow a definite pattern in both sexes. The gonads of both sexes are homologous and indifferent at birth, but within a few days testes and ovaries can be distinguished by the relative size, number and arrangement of the primordial germ cells. No atypical gonads were discovered in the course of this study which would indicate the possibility of sex-reversal.

2. Injections of testosterone propionate induced spermatogenesis in the ovaries, of immature females but had no comparable effect in mature specimens.

3. Injections of estradiol benzoate induced oogenesis in the testes of immature males but had no comparable effect in mature specimens.

4. Improper initial sex classification and hybrid origin of the fish used are suggested as possible explanations for some of the discrepancies between the results obtained in this study and those reported in earlier investigations.

5. The results of the study of the normal sexual development and the attempts to alter the differentiation pattern by experimental means indicate a stable sexual development and differentiation for this species.