BILATERALLY ASYMMETRICAL TESTES IN FISHES OF THE GENUS ORYZIAS

From a comparative morphological viewpoint, we examined the developmen t of gonads of 9 species of teleost fish, genus Oryzias, in which thre e types of bilateral asymmetry were discriminated. The first type occu rs in O. celebensis, O. javanicus, O. marmoratus, O. mekongensis, O. m elastigma, and O. minutillus, in which testes are completely asymmetri cal. Their gonadal rudiments are constructed only on the right side an d develop into testes of a unilobate form. The second type is exhibite d in O. curvinotus and O. luzonensis, where gonadal rudiments appear u nilateral only on the right side. But testicular tissue occurs on the left side of the dorsal mesentery during the development, and adult te stes become bilobate. The testes of O. latipes belong to the third typ e. They initiated from bilateral gonadal rudiments to develop into bil obate testes. These results are almost correspond with the phylogeneti cal classification of Oryzias fishes based on the chromosome morpholog y, indicating that alleles of the gene(s) controlling the symmetry of gonads in these fish originated just after the time when the phylogene tic differentiation occurred. The possible process of the development of the various types of the asymmetrical gonads was discussed.