Ectopic Hermaphroditic Gonad in the Cranial Cavity of Japanese Medaka

Abstract Diseases were monitored for 1 year in a cohort of approximately 560 Japanese medakas Oryzias latipes kept in a laboratory at Tulane University. The fish were maintained as part of a breeding colony for embryological studies. Eighty-six fish exhibiting disease or injury during the year were examined histopathologically. Two adult Japanese medakas (one male and one female) had ectopic hermaphroditic gonads in the cranial cavity. The ectopic gonads were bordered by meninges and cranium. The ectopic gonads in both cases consisted mostly of spermatocytes and spermatids with numerous islands of primary germ cells and a few ovarian follicles. An ectopic gonad in the cranial cavity has not been previously reported in vertebrates.