Illustration of timing of MO effectiveness and toxicant exposure during development. While period of MO effectiveness will vary depending on the synthesis/degradation kinetics of its target gene product, in general, MO persistence will decrease by dilution as development progresses (solid line). How MO effectiveness overlaps with sensitivity to the toxicant being tested (dashed line), when the exposure occurs, as well as when the effect is observed, should all be considered when designing a MO experiment.