Abstract: Objective To explore toxic effects of lead on embryonic development of zebrafish ( EM>Danio rerio/EM>).Methods Zebrafishes (wild type, AB line)were exposed to lead acetate (PbAc) at the doses of 0, 0.1, 0.5, 2.5 and 12.5μmol/L, respectively, from 1 hour post fertilization (hpf) to embryonic hatching or death. There were 50 embryos in each group, and 0 dose group was used as the control. Morphology of the developing embryo was observed with a phase contrast microscope, and the visible toxic effects were recorded. The embryos were photographed at time points of 4, 8, 16, 24, 48 and 72 hpf. The ultrastructure of diencephalon neurons at 36 hpf was observed with a transmission electron microscope. Results The embryonic mortalities of exposure groups were significantly increased compared to the control group ( EM>P/EM> 0.05) with a higher mortality at the early stage of embryonic development. In general, with increasing concentration of PbAc, the mortality increased ( EM>P/EM> 0.01). The aberration rates of the treated embryos were slightly higher than the control group though there was no statistical significance. With the exception of the 12.5 μmol/L lead acetate group, the average hatching times of the exposed groups were longer than that of the control group ( EM>P/EM> <0.05). The results of ultrastructure analysis showed that pathological changes, such as karyopyknosis, cellular edema, and damaged organelles, occurred in the embryonic neuron in the exposed groups.Conclusion Lead may result in considerable toxic effects on zebrafish embryos, especially at the early stage. Low level Pb-exposure may also lead to a

Key words: Lead, Embryonic development, Toxicity, Viviperception, Zebrafish