Fathead Minnow Lifecycle Tests for Detection of Endocrine-Disrupting Substances in Effluents

The goal of this study was to assess the responses of fathead minnows (FHM) exposed to known endocrine-disrupting substances (EDS) in our labs. As well, we wanted to examine the applicability and sensitivity of the full lifecycle FHM test for use on-site, exposing fish to a complex environmentally relevant Canadian effluent. Fathead minnows exposed from the egg stage to ethinylestradiol (EE2, 0–32 ng/L) or methyltestosterone (MT, 0–3200 ng/L) had decreased growth (length, weight) at high concentrations. Development of secondary sex characteristics was a sensitive indicator of exposure to androgen and estrogen. Fish exposed to MT showed premature male sex characteristics such as nuptial tubercles by 30 days post-hatch (dph). These changes were more dramatic in older fish (at 60 and 90 dph), which showed premature male sex characteristics at very low MT concentrations (100 ng/L). Fish exposed to 3.2 ng/L EE2 had premature development of ovipositors at 60 dph. As well, exposure to very high MT concentrations (1000 and 3200 ng/L) caused development of ovipositors after 60 days (but not at 20 and 30 dph), presumably due to aromatization of MT to methylestradiol (as suggested by other researchers). The fathead minnow lifecycle assay, tested with a known estrogen and androgen, proved to be useful for detection of EDS-related changes caused by a real-life effluent mixture. Lifecycle exposures of fathead minnow eggs to bleached sulphite mill effluent (BSME) showed changes in secondary sex characteristics and growth. In contrast to EE2 and MT, fish exposed to BSME had increased growth. Changes in secondary sex characteristics of fish were seen in both male and female minnows exposed to BSME, but there was an overall shift towards increasing numbers of female fish (based on external sex). The full lifecycle assay provides a definitive test for reproductive/EDS effects, and it appears that some of the most sensitive endpoints we studied were the premature development of secondary sex characteristics.