Intercalibration exercise using a stickleback endocrine disrupter screening assay

The OECD is currently in the process of validating a fish screening guideline for endocrine disrupters using three core fish species – Japanese medaka, zebrafish and fathead minnow, and employing three core endpoints – vitellogenin (VTG) induction, gross morphology (secondary sexual characteristics and gonadosomatic index) and gonad histology. None of the core species are indigenous to the UK or other European waters and none of them have an unambiguous, diagnostic endpoint for the detection of androgens and their antagonists. A small inter-laboratory calibration was conducted to generate information on the reproducibility of a stickleback-based method. Three participating laboratories each tested two compounds – the oestrogen 17ß-oestradiol (E2) and the synthetic androgen trenbolone. In the E2 exposure, all three laboratories detected a significant increase in VTG in males after 14 and 21 days at a concentration of 100 ng/L In the trenbolone exposure all three laboratories detected a significant increase in spiggin (the main diagnostic endpoint for androgenic activity) in females after 14 and 21 days at the highest concentration 5000 ng/L. This intercalibration exercise successfully demonstrated that the stickleback is a suitable test species for inclusion in the OECD fish screening guideline, possessing valid, reproducible, diagnostic endpoints for the detection of potent oestrogens and androgens. The OECD has endorsed this work and has requested that, in order to fully align the stickleback method with that of the core species, a larger-scale intercalibration exercise be organised using other, less potent EDCs.