Qualitative and quantitative histomorphologic assessment of fathead minnow Pimephales promelas gonads as an endpoint for evaluating endocrine-active compounds:: A pilot methodology study

Although histopathology is routinely employed as a tool for the detection and assessment of xenobiotic-mediated effects in mammals, it is less frequently applied to fish. In part, this is due to a lack of method standardization regarding study design, tissue preservation, tissue sectioning, histopathological evaluation, reporting, and statistical analysis. The objectives of the present study were: (1) to test and refine a method for the microsurgical excision of fathead minnow (FHM) Pimephales promelas gonads for the purpose of histopathologic examination; (2) to determine the optimal combination of fixation and embedding procedures for the histopathologic and morphometric analysis of FHM gonads following exposure to a known estrogenic compound, 17beta-estradiol (E2); and (3) to provide a method for the categorization and quantification of cell types in FHM gonads by manually counting cells in digitized images using image analysis software. The light microscopic evaluation of individual gametogenic cells was greatly facilitated by specimen preparation techniques that included the excision of gonads via microdissection and by optimized fixation and embedding procedures.