The neuroexcitatory peptide in the venom of the fish-hunting cone snail Conus catus causes rapid tetanic paralysis in its prey. The pathway through which this response is propagated is unknown. However, the speed of the paralysis indicates that retrograde signaling via primary motor neurons and excitatory interneurons is occurring. We use the Zebrafish model to focus on the involvement of a specific type of excitatory interneuron, circumferential descending interneurons. Our goal is to look at the activation of CiD interneurons in situ in the presence of C. catus venom. We are currently able to successfully identify and retrograde label CiDs using calcium green dextran. Furthermore, preliminary data indicates that CiD interneurons are involved in the response to the neuroexcitatory venom peptides, however more trials need to be conducted in order to draw more conclusive results.