Abstract: Ten eleven translocation 1 (TET1) protein is a 5—methylcytosine (5mC) hydroxylase. To study the functions and expression characteristics of TET1 gene in blunt snout bream (Megalobrama amblycephala), the whole mount in situ hybridization (WISH) and qRT-PCR technique were analyzed its expression in embryos and tissues and its response under acute hypoxic stress. Sequence analysis results showed that TET1 gene is 5526 bp, encoding 1841 amino acids. The qRT-PCR results demonstrated that TET1 gene was extensively expressed in tissues of blunt snout bream, especially in brain. During embryonic development, the TET1 gene was expressed from the fertilized egg and was maintained at a high level of 20—44h (20—44 hpf) after fertilization. The WISH analysis results suggested that TET1 signal was relatively weak at 12 hpf, and gradually enhanced at 24 and 36 hpf, especially in the head. Hypoxia significantly induced the expression of TET1 gene in gill, spleen, and other tissues (P<0.01), and significantly decreased its expression in brain, skin, eyes, and kidneys (P<0.01). Hypoxia also increased the expression of TET1 gene in embryos, especially in the 24 hpf hypoxia treatment group (P<0.001). The above results indicated that TET1 gene plays an important role in hypoxia response. This study provides a new perspective on the TET1 gene in terms of hypoxia response and functional conservation and differentiation.