|Abstract||In recent years, increased concern for animal welfare has resulted in the development of the fathead minnow fish embryo toxicity (FET) test as an alternative to the larval growth and survival (LGS) test. Thus far, the greatest limitation in developing and utilizing the fathead minnow FET test has been its inability to identify sublethal adverse effects or predict chronic toxicity, as the only endpoint currently utilized for the FET test is survival. The objectives of this study were to compare the sensitivities of the FET and LGS tests and to evaluate the utility of sublethal metrics as additional endpoints for improving the utility of the FET test. Fathead minnow FET and LGS tests were conducted using three reference toxicants (sodium chloride, ethanol and sodium dodecyl sulfate). Sensitivities for the FET and LGS tests were compared using the median lethal concentration (LC50) estimated by each test for each of the three reference toxicants. Estimated LC50s were not significantly different between FET and LGS tests, indicating a similar ability to assess acute toxicity. In addition to LC50, the FET tests allowed for the evaluation of the effects of sublethal concentrations of the reference toxicants on metrics such as growth, incidence of developmental abnormalities and gene expression. Reductions in fathead minnow mass, increased incidence of pericardial edema, reductions in their ability to hatch and alterations in gene expression for growth and stress at sublethal concentrations of reference toxicants suggest that the predictive power and utility of the FET test could be improved by including these sublethal metrics in toxicity assessments. These results also indicate that the fathead minnow FET test is a viable alternative to the fathead minnow LGS test.