Bilateral efferents from nucleus isthmi to the optic tectum in goldfish (Carassius auratus) are spatially restricted

► The projection from nucleus isthmi to the optic tectum is ambiguous. ► Biocytin deposit in rostromedial tectum labeled ipsilateral neurons in NI. ► The same deposit also labeled a few neurons in the contralateral NI. ► NI projects only ipsilaterally from the remainder of the OT. ► Neurons in the ipsilateral NI are topographic; neurons in contralateral NI are not.