Thermal threshold triggers hepatic immune reprogramming and oxidative exhaustion in large yellow croaker Larimichthys crocea.

Thermal effluents from coastal nuclear power plants (NPPs) typically raise near-field seawater temperatures by 2-4 °C for several hours to days, imposing thermal stress on local marine biota. This study investigates the biochemical and molecular responses of juvenile large yellow croaker Larimichthys crocea to acute thermal stress, simulating the thermal discharges from coastal NPPs. Fish were exposed to 28 °C (control), 29 °C, 30 °C, and 32 °C, with sampling conducted at 24 h and 96 h. At 32 °C, all fish died within 48 h, while exposure to 29 °C and 30 °C for 96 h induced oxidative stress in the liver, marked by elevated lipid peroxidation and altered antioxidant enzyme activities. Transcriptomic analysis showed a significant intensification of immune responses after 96 h compared to 24 h at both 29 °C and 30 °C. Notably, immune response adaptation occurred at 29 °C, whereas at 30 °C, immune-related pathways shifted from pro-inflammatory activation to broad transcriptional suppression as the temperature approached the species' upper thermal limit. These findings highlight the narrow thermal tolerance of L. crocea, provide insights into the risks of thermal pollution from NPPs, and emphasize the need for improved coastal aquaculture management to address the impacts of climate change and ocean warming.