Although hypoxia-inducible factor (HIF) 1 alpha and 2 alpha function as master regulators of the transcriptional response to hypoxia, the function of HIF3 alpha and its responses to hypoxic stress remain unclear in teleost fish. Here, we characterized the HIF3 alpha cDNA in hypoxia-sensitive blunt snout bream (Megalobrama amblycephala), with 3059 bp length, consisting of an open reading frame (ORF) encoding 643 amino acid residues. Blunt snout bream HIF3 alpha mRNA was stably expressed during stages of embryonic development and in adult tissues. After a 4 h hypoxia stress, HIF3 alpha mRNA of the juvenile fish was significantly upregulated in the liver, brain, and kidney, and restored to the pretreatment levels after a 24 h recovery. When tagged with enhanced green fluorescent protein (EGFP) and transfected into cultured HeLa cells, blunt snout bream HIF3 alpha was mainly distributed in the nucleus under normoxia. Treatment of the cells with CoCl2 to mimic hypoxic conditions showed that there was no effect about the nuclear localization of HIF3 alpha but a statistically significant increase in HIF3 alpha protein levels. A nuclear localization signal (NLS) sequence at the C-terminus of HIF3 alpha may exert positive effects in the process of nuclear localization. These results suggest that blunt snout bream HIF3 alpha could be involved in different physiological functions under normoxia and hypoxia conditions. (C) 2018 Elsevier Inc. All rights reserved.