The is a commercially important anadromous species distributed mainly in the Yangtze River of China and in coastal waters of China, Korea and Japan. The species is popularly known locally as one of the three most delicious fishes in the Yangtze River, along with the obscure pufferfish; additionally, is the main source of income for many Yangtze River fishermen. migrates to sea for growth and so experiences a wide range of salinities, making osmoregulation especially important for the species during this migration. The protein aquaporin-1 (AQP1), a member of the aquaporin family of integral membrane proteins, functions in transporting water as well as ammonia, urea and glycerin. Accordingly, it is important for hypertonic and hypotonic regulation and maintaining osmotic homeostasis in an organism. To investigate the osmoregulatory role of AQP1 in , we used rapid amplification of complementary DNA (cDNA) ends (RACE method) to clone, for the first time, aquaporin-1 from this species. The full-length cDNA covered 1 299 base pairs (bp) with a 777 bp open reading-frame (ORF) within the 5' untranslated region (UTR) of 107 bp and the 3'UTR of 458 bp. The ORF encoded 258 amino acids, with a calculated molecular mass of 27.1 kDa, and theoretical isoelectric point of pH 6.13. The results show that AQP1 of possesses typical conserved domains of the AQP family, including six transmembrane helices and two NPA (Asn-Pro-Ala) motifs, and one binding site for mercury (II) chloride (HgCl₂), which is an AQP1 inhibitor. Next, we analyzed the homology and phylogenetic systematics of the AQP1 sequence from . The highest homology and similarity (reaching 93%) occurred between the AQP1 of . The AQP1 of displayed an evolutionary relationship the furthest from AQP1 of mammals. We performed real-time quantitative PCR (qPCR) to study the expression of AQP1 in various tissues of , namely gill, brain, mid-kidney, anterior intestine, posterior intestine, spleen, liver, heart and muscle. The results showed that it expressed in many of the tissues (including gill, mid-kidney, anterior intestine, posterior intestine, liver and muscle), but the level of expression was highest in the brain. Lastly, we performed a high-salinity stress test to discover the osmoregulatory function of AQP1 in under conditions of hypertonic stress. The expression of AQP1 in gill, mid-kidney, anterior intestine, and posterior intestine significantly differed from that in tissues of the controls (<0.05). These results demonstrate that AQP1 indeed plays an important role in osmoregulation in , and the study provides a theoretical reference for further research on the metabolic costs of osmoregulation in .