| Water breathing teleost fish have serotonin-containing neuroepithelial cells (NECs) in the gills that respond to hypoxia, but little is known about oxygen sensing in amphibious fish. The mangrove killifish, Kryptolebias marmoratus, is an amphibious fish that respires via the gills and/or skin. I tested the hypothesis that the gills and skin have hypoxia-sensitive NECs and these cells are involved in the hypoxia response in K. marmoratus . NECs were present in both gills and skin and the NEC area but not density increased significantly following chronic exposure to hypoxia. Acute exposure to hypoxia induced fish to emerse at 0.2 mg˙L-1 dissolved oxygen. When K. marmoratus were pre-exposed to serotonin or acetylcholine, they emerse at a significantly higher concentration of oxygen than untreated fish. Exposure to blockers for serotonin or muscarinic acetylcholine receptors (ketanserin and hexamethonium, respectively) resulted in fish emersion at a lower concentration of oxygen. Taken together, these results suggest that oxygen sensing may occur on the branchial and cutaneous surfaces in K. marmoratus and that serotonin and acetylcholine, in part, mediate the emersion response. |
