Physiological, Histological, and Molecular Responses of White Trevally (Pseudocaranx dentex) to Acute Hypoxia

Dissolved oxygen (DO) is a key environmental factor affecting the survival and development of farmed fish. However, the hypoxia responses of white trevally (Pseudocaranx dentex) remain poorly understood. In this study, we determined the DO tolerance thresholds and integrated physiological, histological, and molecular responses of white trevally to hypoxic stress. Smaller fish exhibited higher values for critical oxygen tension (3.50 ± 0.18 mg/L) and loss of equilibrium (LOE, 0.92 ± 0.14 mg/L), whereas larger fish showed lower values. Hypoxia significantly elevated serum cortisol, glucose, alanine aminotransferase, and aspartate aminotransferase levels, which peaked at LOE. Under hypoxia, histological analysis revealed lamellar clubbing, hypertrophy, and hyperplasia in gills, and vacuolization and nuclear migration in liver sections. In the liver, superoxide dismutase and catalase activities and malondialdehyde content increased, while glutathione peroxidase activity decreased. Upregulation was observed for stress-related genes (HSP70, HSP90, mineralocorticoid receptor, and glucocorticoid receptor) and pro-apoptotic genes (p53, BAX, and Caspase-3), while Bcl-2 was downregulated. Principal component analysis indicated that hypoxia triggered stress responses, tissue damage and apoptotic signaling; smaller fish were the most vulnerable, emphasizing the need for size-specific management in aquaculture. Collectively, these findings provide baseline data that may support the healthy development of traditional white trevally aquaculture.