The goal of present study is to determine whether metals or nanomaterials are transferred from exposed pregnant females of viviparous fishes to their developing offspring and the subsequent potential effects on the oxidative stress and histomorphological indicators. Gravid females of guppies (Poecilia reticulata) exposed to 1 mg/l copper sulfate (CuSO₄) or copper oxide nanoparticles (CuO-NPs) for 17 to 25 days depending on giving birth. Once a female gave birth, the female and her newborn offspring were analyzed for copper concentrations while some oxidative stress parameters and histopathology were performed for the newborn offspring. There were no malformations or histopathological lesions observed in the newborn offspring of guppies exposed for either CuSO₄ or CuO-NPs. Also, there was no maternal metal transfer for either CuSO₄ or CuO-NPs while females exposed to copper sulfate only showed significantly higher concentrations of Cu compared to control group. In addition, there were non-significant changes in catalase compared to control group. While, glutathione decreased significantly in offspring their mothers exposed to CuO-NPs only compared to control group. In addition, superoxide radical and lipid peroxidation increased significantly in offspring their mothers exposed to CuSO₄only compared to control group. The findings of the present study indicated that the offspring were more sensitive to CuSO₄ than CuO-NPs. Although absence of metal Cu in the tissues of offspring as well as lack of morphological abnormalities and histopathology, maternal transfer of Cu metabolites may be suggested to be the causative factor for some oxidative stress.