Abstract: Water temperature is an important factor affecting the physiological functions of fish. Gills are the primary respiratory organs of fish, and their physiological homeostasis is crucial for organismal health. To investigate the physiological response in the gills of Trachinotus ovatus juveniles to high temperature stress, we set up a control group (29 ℃) and a high temperature group (34 ℃), and the stress experiments lasted for 7 d. We investigated the oxidative stress indicators using biochemical methods, and studied the expression of genes related to stress response, inflammation, immunity, apoptosis, osmoregulation, and the mitochondrial respiratory chain using qPCR. The results show that: 1) The oxidative stress indicators, such as the activities of total antioxidant capacity (T-AOC), anti-hydroxyl radical capacity (AHC) and anti-superoxide anion capacity (ASC) decreased significantly. 2) The stress response indicators, such as the expression level of hypoxia inducible factor-1α (HIF-1α) gene decreased significantly. 3) The inflammatory indicators, such as the expression levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and transforming growth factor-β (TGF-β) genes increased significantly, while the expression levels of interleukin-8 (IL-8), interleukin-10 (IL-10), nuclear factor-κB (NF-κB) and IκB kinase (IKK) genes decreased significantly. 4) The immune indicators, such as the expression levels of immunoglobulin T (IgT) and immunoglobulin M (IgM) genes decreased significantly. 5) The apoptosis indicators, such as the expression level of caspase-9 (Casp-9) gene increased significantly, while the expression level of caspase-3 (Casp-3) gene decreased significantly. 6) The osmoregulatory indicators, such as the expression levels of Na⁺/K⁺-ATPase-α (NKA-α) and aquaporin-1α (AQP-1α) genes did not change significantly. 7) The mitochondrial respiratory chain indicators, such as the expression level of cytochrome c oxidase subunit I (COI) gene increased significantly. These results demonstrate that high temperature stress can disrupt the physiological homeostasis in the gills of T. ovatus by inducing oxidative stress and inflammatory responses, and affecting the functions of immunity, apoptosis, osmoregulation and respiratory chain.