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(18-61) Quantifying the ontogeny of gonad development in sexually maturing fathead minnows (Pimephales promelas). Panter, Grace*,1, Hutchinson, Thomas2, Sumpter, John3, van Aerle, Ronny4, Tyler, Charles4, 1 CEFIC-EMSG; c/o AstraZeneca Global Safety, Health & Environment, Brixham, Devon2 AstraZeneca Global Safety, Health & Environment, Brixham, Devon3 Brunel University, Uxbridge, Middlesex4 Exeter University, Exeter, Devon ABSTRACT- An in vivo screening assay, using juvenile fathead minnows (Pimephales promelas), was developed to detect a range of endocrine active substances (EAS). This assay proved to be highly successful for screening EAS with both anti-oestrogenic and oestrogenic activity. However, it was concluded that fish used in the screen (weighing 150±30 mg) were too small for detecting all classes of EAS. Our current research is aimed at establishing the appropriate fish life-stage for identifying EAS with (anti-)aromatase activity and other steroidogenic enzyme activities. To do this we needed to define the ontogeny of sexual development in maturing fathead minnows in order to identify the most appropriate window(s) for studies on such substances. Results indicated that in the males, the testis grew at a steady rate during the study period (60 to 201 days post-hatch(dph)). However, in the females there was a period of rapid gonad growth immediately prior to the onset of spawning at 88 dph. Just preceding this rapid increase in gonad growth there was a dramatic elevation in plasma vitellogenin (VTG) concentrations. Histological examination of the gonads enabled the stage of gonad development to be determined in individual fish and to ascertain if a link could be made between developmental stage, fish size and plasma VTG concentration. The results, on the basic cycle of gonad reproductive development in sexually maturing fathead minnows, will provide the framework of information for use in determining the developmental stages of fish most appropriate for screening certain classes of EAS. Key words: fathead minnow, gonad development |
