Glucose transport across the plasma membrane is mediated by a family of glucose transporter proteins (GLUTs), several of which have been identified in mammalian, avian and, more recently, in fish species. Here we report on the cloning of a salmon GLUT from adipose tissue with a high sequence homology to mammalian GLUT4 and which has been named okGLUT4. Kinetic analysis of glucose transport following expression in Xenopus laevis oocytes demonstrated a 7.6 ± 1.4 mM Km for 2-deoxyglucose (2-DG) transport measured under zero-trans conditions and 14.4 ± 1.5 mM by equilibrium exchange of 3-O-methylglucose. Transport of 2-DG by okGLUT4-injected oocytes was stereospecific and was competed by D-glucose, D-mannose and, to a lower extent, D-galactose and D-fructose. In addition, 2-DG uptake was inhibited by cytochalasin B and ethylidene glucose. Moreover, insulin stimulated glucose uptake in Xenopus oocytes expressing okGLUT4 and in isolated trout adipocytes, which contain the native form of okGLUT4. Despite differences in protein motifs important for insulin-stimulated translocation of mammalian GLUT4, okGLUT4 was able to translocate to the plasma membrane from intracellular localization sites in response to insulin when expressed in 3T3L1 adipocytes. These data demonstrate that okGLUT4 is a structural and functional fish homolog of mammalian GLUT4 but with a lower affinity for glucose, which could in part explain the lower ability of fish to clear a glucose load.