This study cloned the hemoglobin a1 from the marine teleost, the half-smooth tongue sole （Cynoglossus semilaevis）, and then examined its expression under hypoxia exposure. The full-length of CsHb-a1 （594 bp） cDNA contains an open reading frame encoding 144 amino acids. Sequence analysis shows that the predicted CsHb-a1 amino acids shares high identities with that of other species. Real-time PCR showed that CsHb-a1 was highly expressed in the heart, liver, spleen, kidney and blood. Five to 120 min esposure and long-term （36 h） exposure to hypoxia （1.0 mg/L） significantly increased CsHb-a1 mRNA expression in most tissues compared to those fish held in normoxic conditions （dissolved oxygen （DO）： 6.2 mg/L）. These results suggested that the up-regulation of Hb-a1 is an important component for adaptation of half-smooth tongue sole to short-term hypoxia.
