We have chosen zebrafish as an alternative vertebrate model so that we could take advantage of its embryonic growth outside the mother, its small size, and the ability to visualize development as it is happening. We have used these characteristics in combination with transgenic technologies to visualize gene regulation and the anatomical development of different parts of the embryo. In this presentation we will point out the homologies between retinoid signaling in zebrafish versus mouse and we will also introduce the model as a tool for investigating adult behavioral changes caused by embryonic exposure to chlorpyrifos.