MP13 Aquatic Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(LOT-1117-824376) Evaluation of Gonadal Histopathology in Spawning vs. Non-Spawning Medaka.

Lothenbach, D.¹, Ankley, G.¹, Johnson, R.¹, ¹ USEPA Mid-Continent Ecology Division, Duluth, MN, USA

ABSTRACT- Recently, the U.S. Environmental Protection Agency has been involved in an international cooperative effort with the Organization of Economic Cooperation and Development (OECD) to develop fish screening assays capable of detecting endocrine-disrupting chemicals. One proposed OECD assay involves a non-spawning protocol with adults for the detection of androgenic or estrogenic chemicals. Responses considered to be indicative of estrogenic and androgenic effects include changes in vitellogenin, secondary sex characteristics, gonadosomatic index (GSI) and/or gonadal histopathology. To initiate the test, actively-spawning fish are placed in each aquarium but are prevented from further spawning by isolating males from females. After two weeks of acclimation without chemical, fish are exposed for 21-days, euthanized and sampled. In several non-spawning tests, gonad histopathology was ambiguous because of substantial gonadal pathology in the controls. It was hypothesized that much of the pathology observed was caused by retention of mature oocytes following the cessation of spawning. This study assessed the effect of spawning termination by gender segregation on gonad histopathology. Six aquaria, each containing 6 male and 6 female medaka (Oryzias latipes) were setup as specified by the OECD non-spawning assay. Fish in three aquaria were maintained in the non-spawning state and fish in the remaining three aquaria were not segregated and allowed to continue spawning. After 21 days, the fish were sacrificed and their gonads examined for histopathology. The ovaries of non-spawning females contained a large number of ovulated oocytes and only a few stage four oocytes. Many of the ovulated oocytes were at the initial stages of atresia. Ovaries from spawning females were primarily at stage 3 or 4, and contained oocytes at all stages of development. These results suggest that the experimental design used for the non-spawning protocol can cause artifactual alterations suggestive of endocrine disruption in ovarian tissue.

Key words: oryzias latipes, endocrine, pathology, EDC