title: Intersex in Japanese medaka (Oryzias latipes) used as negative controls in toxicologic bioassays: a review of 54 cases from 41 studies.
abstract: Histologic assessment of the gonads to detect intersex has become a valuable end point in reproductive toxicologic testing for fish, and many studies have solidly linked intersex with exposure to endocrine active substances (EAS). An assumption in such studies is that spontaneous intersex does not occur in control fish. Using historical data derived from toxicologic tests with Japanese medaka (Oryzias latipes), we report a retrospective study in which we identified 54 individual instances of intersex (testicular oocytes or ovarian testicular tissue) in control medaka from 15 of 41 selected toxicologic studies. These studies, comprised of previously unpublished data, had been conducted at three geographically distant laboratories, each of which utilized unique water sources, employed somewhat different culture protocols, and maintained distinct medaka breeding colonies. During our histologic examinations, we also identified three germ cell neoplasms that had been inadvertently diagnosed as intersex. In the present report, we review potential causes of intersex, discuss possible reasons why spontaneous intersex has rarely been reported, and propose suggestions for the judicious interpretation of intersex results in medaka studies involving EAS.
authors: U.S. Environmental Protection Agency, Office of Science Coordination and Policy, 1201 Constitution Avenue, Northwest, EPA East Building 4121M, Washington, DC 20004, USA.
authors: K Christiana
authors: KC
authors: Grim
authors: Marilyn
authors: M
authors: Wolfe
authors: William
authors: W
authors: Hawkins
authors: Rodney
authors: R
authors: Johnson
authors: Jeffrey
authors: J
authors: Wolf
mesh_terms: D000818:Animals; D001681:Biological Assay; D052244:Endocrine Disruptors / Q000633:toxicity*; D005260:Female; D005843:Geography; D008297:Male; D009373:Neoplasms, Germ Cell and Embryonal / Q000473:pathology; D009990:Oryzias; D010053:Ovary / Q000187:drug effects* / Q000473:pathology / Q000502:physiology; D012726:Sexual Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D013737:Testis / Q000187:drug effects* / Q000473:pathology / Q000502:physiology; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D052244:Endocrine Disruptors; D014874:Water Pollutants, Chemical