Pyraoxystrobin is a novel strobilurin fungicide with excellent and broad spectrum antifungal efficiency.However,the toxic effects of pyraoxystrobin on fish are still limited.In the present study,zebrafish,during embryos,larvae and adult stages,was selected to assess the acute and developmental toxicity of pyraoxystrobin,and the potential mechanism was explored.Mortality,behavior abnormity,developmental endpoints and teratogenic effects were measured.Meanwhile,the expression of genes related to oxidative stress,cell apoptosis and immune response was also detected.The results showed that the 96-h LC50 values of pyraoxystrobin to embryos,12 h post-hatching(hpf)larvae,72hpf,and adult fish were 4.099、1.069、3.236 and 5.970 μg/L,respectively,suggesting that zebrafish of early life stages were more sensitive to pyraoxystrobin than adult stage.In embryo toxicity test,the heartbeat at 48 and 72 hpf,hatching rate and body length of larvae at 96 hpf was significantly inhibited by pyraoxystrobin.Besides,a series of morphological deformities were observed,including pericardial edema,yolk sac edema and spine deformation.The rate of malformation increased in a time-and concentrationdependent manner.Furthermore,the mRNA expression of manganese superoxide dismutase(Mn-Sod)and glutathione peroxidase(Gpx)were markedly up-regulated yet catalase(Cat)was inhibited notably.In addition,the key genes involved in cell apoptosis pathway(e.g.P53,Apaf1,Bcl2,Bax and Cas3)were all significantly down-regulated at 3μg/L of pyraoxystrobin.The mRNA levels of main cytokines including tumor necrosis factor a(Tnfα),interferon(Ifn)and interleukin-1 beta(Il-1β)were also obviously up-regulated,suggesting that the innate immune system might be disturbed by pyraoxystrobin.In summary,the results of present study indicated that pyraoxystrobin was highly toxic to zebrafish and could cause developmental toxicity on embryos.The disturbance of pyraoxystrobin on expression of oxidative stress-,apoptosis-and immune-related genes might be responsible for the toxicity.However,to confirm the conclusion,further study on the toxicity mechanisms of pyraoxystrobin to zebrafish is still needed.