This Test Guideline describes an in vivo screening assay for fish reproduction where
sexually mature male and spawning female fish are held together and exposed to a chemical
during a limited part of their life-cycle (21 days). The short term reproduction assay
was validated in the fathead minnow (Pimephales promelas) and this is the recommended
species. The assay is run with three test chemical concentrations and the necessary
controls, including a carrier control if necessary. For the fathead minnow, four replicate
test vessels are used for each treatment level and control(s). During the conduct
of the assay, the egg production is measured quantitatively daily in each test vessel.
At termination of the 21-day exposure period, two biomarker endpoints are measured
in males and females separately, as indicators of endocrine activity of the test chemical;
these endpoints are vitellogenin and secondary sexual characteristics. Gonads of both
sexes are also preserved and histopathology may be evaluated to assess the reproductive
fitness of the test animals and to add to the weight of evidence of other endpoints.