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(T/EH035) Sexual development in the fathead minnow: Baseline studies for developing OECD test guidelines for endocrine disrupting chemicals. Panter, Grace1, Hutchinson, Thomas2, Hurd, Kate2, Pounds, Nadine2, Tyler, Charles3, 1 2 3 ABSTRACT- Research to date, has shown that vitellogenin induction/inhibition in juvenile fathead minnows (Pimephales promelas)(150 ± 30 mg) is suitable for the detection of estrogenic/antiestrogenic chemicals. This life-stage, however, will not be relevant for assessing the effects of all classes of endocrine disrupting chemicals. The European Chemical Industry is supporting the development of a juvenile fathead minnow screening assay. Current research is aimed at defining the most relevant periods of gonad development and lfe-stage selection to study the effects of specific groups of hormone mimics/disrupters. However, some chemicals are now known to disrupt steroid enzyme pathways, which in turn can alter steroid biosynthesis and degradation. A key enzyme of concern is aromatase which converts testosterone to estrogen. In this study the ontogeny of sexual development is being studied with a view to defining the most appropriate window for studies on chemicals that interefere with aromatase expression/activity. Newly fertilised eggs were reared according to OECD test guideline 210 (flow-through; 25°C) for an extended period of up to 56 days post hatch (dph). At 57 dph fish were maintained following test guidelines detailed in EPA 540/9-86-137 (flow-through; 25°C). At 60 dph and every seven days thereafter until the fish were sexually mature, 25 fish were sacrificed, a plamsa sample frozen for vitellogenin determination, and the gonads fixed in Bouins for histological analyses of gonad development. In parallel, at each sampling time point 12 fish were sacrificed, their brains and gonads snap frozen to determine aromatase mRNA expression. Key words: Fathead minnow, Gonad development |
