Thermal stress disrupts development, physiology, and immune responses in large yellow croaker (Larimichthys crocea)

Thermal stress from global warming and heated discharges from coastal nuclear power plants poses a significant threat to marine aquaculture, particularly during the sensitive early life stages of fish. These discharges elevate local seawater temperatures, altering the nearshore thermal environment. This study examined the effects of elevated temperatures on early development in large yellow croaker (Larimichthys crocea), a commercially important mariculture species in China. Embryos were exposed to five temperature regimes (22, 23, 24, 26 and 28 °C) to evaluate impacts on hatching success, survival, morphology, physiology, antioxidant activity, and immune gene expression. Temperatures +4 °C and +6 °C above the optimal 22 °C significantly reduced survival and body length, induced early hatching, and increased deformities. Antioxidant enzyme activity declined, while malondialdehyde (MDA) levels rose, indicating oxidative stress. Expression of heat shock proteins showed a selective response, with hsp70 downregulated and hsp27 upregulated. Immune-related genes such as nfkb and casp1 were upregulated, while infy, myd88, and tgfb were suppressed. The integrated biomarker response version 2 (IBRv2) quantified cumulative biological stress across treatments. These findings provide insight into the temperature sensitivity of early developmental stages in marine fish and emphasize the importance of thermal assessments under changing environmental temperature conditions.