Abstract
A new quantitative evaluation technique called the fragmented method* for the detection of testis-ova in male fish using a medaka (Oryzias latipes) S-rR strain has been developed in this study. A current histological method is still being applied to detect the testis-ova in male fish exposed to estrogens or suspected endocrine-disrupting chemicals, even though some disadvantages, such as oversight of the testis-ova due to the limited observation area of the testis, are apparently indicated. The method we developed here enables the accurate determination of the number and the developmental stages (size) of oocytes in a whole testis. The testis was removed from the specimen, fixed with 10% buffered formalin solution and broken into small fragments with a dissecting needle and aciform forceps in glycelin solution containing a small amount of methylene blue or toluidine blue on a slide glass. All developing oocytes of various sizes were clearly stained and thereby were observable under a dissecting microscope. Spermatozoa were also distinguishable in this method. In conclusion, this method is not only proven as a convenient and cost-effective method for quantitatively detecting testis-ova appearance in fish, but is also expected to contribute to the understanding of testis-ova appearance and its biological significances to future studies of endocrine disruption.
*The fragmented method is a new technique for quantitatively detecting testis-ova in male fish using the medaka (Oryzias latipes) strain described in this paper. This technique was developed in the research that the National Institute of Advanced Industrial Science and Technology (AIST) entrusted to Sumika Technoservice Corporation.
