Adequate oxygen delivery to tissue is important for maintaining cellular homeostasis. Thus, an animal’s ability to detect low oxygen is crucial for survival. In fish, oxygen sensing occurs in the gills via chemoreceptive neuroepithelial cells (NECs). Despite the many similarities between NECs and mammalian chemoreceptors, the receptors and neurochemistry involved in gill hypoxia signalling have not been well defined. The goals of the present study were to delineate a mechanism by which presynaptic dopamine D2 receptors modulate the chemoreceptor response to hypoxia, and to begin exploring receptors involved in the excitatory transmission of hypoxia within the zebrafish gill. Using an isolated gill preparation from Tg(elavl3:GCaMP6s) zebrafish, we found NECs respond to hypoxia by an increase in Ca2+i and activation of presynaptic dopamine D2 receptors with the selective agonist, quinpirole, decreased the calcium response to hypoxia. Presynaptic modulation via D2 receptors led to a decrease in the activity of postsynaptic neurons that innervated NECs during hypoxia. Further evaluating the postsynaptic responses to hypoxia, we demonstrated activation of these neurons with acetylcholine, and the neuronal response to hypoxia was reduced by addition of hexamethonium, a nicotinic acetylcholine receptor antagonist. Our results provide the first direct evidence of neuromodulation of the hypoxic signal produced by NECs in the gill by dopamine, suggesting that a modulatory role for dopamine in oxygen sensing arose early in vertebrate evolution. Further, we suggest a role for acetylcholine in the transmission of the hypoxic response, further highlighting the similarity between NECs and mammalian chemoreceptors.