Eggs/larval of freshwater fish (Danio rerio) were exposed to low dose rates of external gamma radiation (from 1 to 1000 mGy d -1) over a 20-day period, with the objective of testing the appropriateness of the 10 mGy d -1 guideline suggested by the IAEA. The present study examines different endpoints, mortality and hatching time and success of embryos as well as the genotoxicity of \textgreekg-irradiations (after 48 h). The 20-day embryo-larval bioassay showed an enhanced larval resistance to starvation after chronic exposure to \textgreekg irradiation (from low 1 mGy d -1 to high dose rate 1000 mGy d -1) and an acceleration in hatching time. Gamma irradiation led to increased genotoxic damage Ito zebrafish egg (40-50% DNA in tail in Comet assay) from the lowest dose rate (1 mGy d -1). Possible mechanisms of \textgreekg radiotoxicity and implications for radioprotection are discussed. © 2011 Elsevier Ltd.