Differential tissue-specific thermotolerance and cellular recovery mechanisms in Haliotis discus hannai under thermal stress

Rising seawater temperatures and marine heatwaves threaten abalone aquaculture, causing significant “summer mortality”. The present study systematically investigates tissue-specific thermal stress responses in Pacific abalone ( Haliotis discus hannai ), comparing intestine, gill, mantle, muscle, and digestive gland under gradient heating (1°C/h) and instantaneous heating. Biochemical and molecular analyses revealed distinct tissue sensitivities. Gill tissue exhibited the highest thermal sensitivity, showing significant oxidative damage (elevated malondialdehyde, p  < 0.05) and heat shock protein ( hsp70 , hsp90 ) upregulation at 28°C. In contrast, muscle tissue demonstrated resilience, maintaining stable antioxidant enzyme (SOD, CAT) activity. Instantaneous heating triggered earlier stress responses than gradient heating: glucose, lactate dehydrogenase (LDH), and total antioxidant capacity (T-AOC) increased significantly at lower temperatures ( p  < 0.05). Gill tissue showed pronounced endoplasmic reticulum stress ( xbp1 splicing) and hsp70 expression at 24°C under instantaneous heating, whereas other tissues responded only at higher temperatures. During recovery, hsp70 expression in gills rapidly declined post-stress, while intestine and mantle exhibited delayed recovery. TUNEL assays revealed temperature-dependent apoptosis in mantle and digestive gland at ≥ 24°C, whereas gill and muscle displayed minimal DNA damage. These results provide physiological benchmarks for monitoring abalone health under temperature fluctuations, with implications for aquaculture management during extreme climate events.