Ovo-testis is a type of intersex or hermaphroditism, where ovarian and testicular tissue are present in the same gonad. It differs from testis-ova, where oocytes are observed scattered in the testis. The two examples of ovo-testis shown here were observed in a multigeneration exposure study by Jon Nash1, in a group that had lifetime exposure of F0 and F1 zebrafish to a low concentration of ethynylestradiol (EE2; 5 ng/L, equivalent to 0.017 nM).
The ovarian part in the first sample was small but well developed (upper image), containing all stages of oocyte maturation. The testicular part in this specimen was small and underdeveloped; it contained a relative low amount of mature sperm, compared to normal male zebrafish
The ovarian part in the second sample (lower image) was rudimentary: it was small and contained only very early stages of oocyte maturation. The testicular part of the gonad in this specimen had a normal size, but also contained a relative low amount of mature sperm. In both cases, the ovarian and testicular tissue occurred bilaterally in a distinct organisation, although there was an occasional small oocyte within the testicular tissue.
Note: a possible confusing image is that of testicular calculi.
- Nash JP, Kime DE, Van der Ven LT, Wester PW, Brion F, Maack G, Stahlschmidt-Allner P, Tyler CR. Long-term exposure to environmental concentrations of the pharmaceutical ethynylestradiol causes reproductive failure in fish. Environ Health Perspect.112:1725-1733; 2004.