Precise quantification of radiation damage in a biological entity in a timely manner is a major challenge in radiobiology. Bioassays are often carried out hours, days or even years after exposure, when the body has already elicited its intrinsic cellular repair mechanisms, rendering the assays only detecting results of recovery instead of the situation at the point of exposure. This is particularly true when quantifying low-dose ionizing radiation damage, as the amount of damage could be quickly reduced to minimum or basal level if the narrow time window is missed. Our group utilizes zebrafish to understand ionizing radiation damage towards biological organisms. By exploiting the optical transparency and genetic amenability of zebrafish embryos, we aim to understand the real-time spatiotemporal dynamics of molecular and cellular events happening when an intact organism is exposed to ionizing radiation.