The fathead minnow extended one generation reproduction test (FEOGRT): A design for regulatory application

The fathead minnow (Pimephales promelas) is a well-established test species for aquatic (eco-) toxicology testing, including regulatory use in fish life-cycle toxicity tests and tests for endocrine disruption. Given its extensive use and available supporting historical data, the fathead minnow extended one generation reproduction test (FEOGRT) under discussion is similar in test design to the Japanese medaka (Oryzias latipes; MEOGRT) and zebrafish (Danio rerio; ZEOGRT) extended one generation tests. This test incorporates key life stages and endpoints across three generations, enabling detection of both manifest and potential transgenerational toxicity. It includes mechanistic information on endocrine sensitive parameters, such as vitellogenin, male secondary sex characteristics, sex ratio and gonadal histopathology, and parameters useful for assessing adversity (i.e., growth, development, and reproduction). The FEOGRT design is six weeks longer in duration than the MEOGRT and requires more fish (<50%) compared to alternative "EOGRT" test designs; however, it does offer several advantages. The fathead minnow is a common model used in lower-tier testing (e.g., fish short-term reproduction assay or fish early-life-stage test). For example, existing datasets can inform on the FEOGRT, which often negates the requirement for additional range-finding studies, offers species concordance, and increases the options for testing laboratories. The fathead minnow is often preferred over fish species such as zebrafish and medaka due to its ease of culturing and handling, extensive validation in test guidelines, laboratory experience, clear external secondary sex differences, and the availability of historical control data. The proposed FEOGRT design does not require extensive validation since it follows adopted test guidelines in which the fathead minnow is already a recommended test species. The findings of the current review consider that the FEOGRT is a robust and regulatory-acceptable test, comparable to MEOGRT and ZEOGRT, offering a useful approach for assessing reproductive and endocrine toxicity in fish.