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Progress Towards the Development of a Fathead Minnow Embryo Test and Comparison to the Zebrafish Embryo Test for Assessing Acute Fish Toxicity
Citation:
Rawlings, J., S. Bohler, M. Jeffries, A. Stultz, J. Oris, T. Braunbeck, T. Norberg-King, AND S. Belanger. Progress Towards the Development of a Fathead Minnow Embryo Test and Comparison to the Zebrafish Embryo Test for Assessing Acute Fish Toxicity. Presented at Society for Toxicology and Chemistry, November 11 - 15, 2012.
Impact/Purpose:
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Description:
The Zebrafish Embryo Test (ZFET) for acute fish toxicity is a well developed method nearing adoption as an OECD Test Guideline. Early drafts of the test guideline (TG) envisioned a suite of potential test species to be covered including zebrafish, fathead minnow, Japanese Medaka, rainbow trout, and potential marine species such as sheepshead minnow. However, during TG discussions, it was also clear that zebrafish was most well studied, clear recommendations on all key aspects were sufficient for guideline development and many laboratories were using the ZFET. All other species lagged behind. Experience with ZFET formed the foundation for new progress to develop a similarly robust fathead minnow guideline that may find utility in geographies that commonly use this species. In this poster we review key developments regarding method details on developmental milestones, time to first feeding, influence of temperature, and a limited set of information on comparative sensitivity using reference compounds and other chemicals. In general, breeding and subsequent harvesting of eggs is somewhat more time intensive and variable with fathead minnow. The time to hatch at equivalent environmental temperatures is approximately a day longer for fathead minnows. Transition from endogenous (yolk sac) to exogenous feeding (procurement of external food items) that marks the end of the eleutheroembryo stage is somewhat later in fathead minnow. Fathead minnows are in the eleutheroembryo life stage minimally for 24 h post hatch and as long as 42 h post hatch depending on the time to hatch (fathead embryos that hatch later tend to feed exogenously earlier). Comparative toxicity using the model compound 3,4-dichloroanaline (DCA) suggests fathead minnows are approximately 3 times more tolerant to DCA than zebrafish. A limited comparative data set indicates that sensitivities are largely overlapping with neither species being uniquely tolerant or sensitive. It is our opinion that a