Acute heat stress induces tissue histopathology, hepatic oxidative stress, and apoptosis in black rockfish (Sebastes schlegelii).

Global climate change and rising temperatures pose a serious threat to the survival of aquatic ectotherms. To analyze the physiological response of black rockfish (Sebastes schlegelii) to acute heat stress, this study investigated its comprehensive adaptation mechanisms under thermal challenge. The levels of biochemical parameters in plasma and liver were assessed, while histological morphology was analyzed via hematoxylin-eosin staining. Cell apoptosis was assessed by TUNEL assay and the expression of related genes was detected by using qPCR. Results showed that exposure to high temperature significantly elevated red blood cell counts (from 1.46 ± 0.10 to 2.50 ± 0.15 × 1012/L, P < 0.05), white blood cell counts (from 191.80 ± 5.46 to 219.97 ± 4.58 × 10⁹/L, P < 0.05), hemoglobin (from 92.00 ± 6.48 to 119.67 ± 11.15 g/L, P < 0.05), hematocrit (from 30.83 ± 1.11 to 38.87 ± 1.61%, P < 0.05), serum glucose (from 1.80 ± 0.20 to 3.63 ± 0.15 mmol/L, P < 0.05), and cortisol levels (from 3.52 ± 0.46 to 10.16 ± 1.02 ng/mL, P < 0.05). The secondary lamellar length, width, basal epithelial thickness, and perimeter of gills were increased (for length: from 224.43 ± 2.36 to 240.90 ± 4.56 μm, P < 0.05; for width: from 14.93 ± 1.50 to 21.57 ± 5.06 μm, P < 0.05; for basal epithelial thickness: from 24.30 ± 1.73 to 32.57 ± 2.97 μm, P < 0.05; for perimeter: from 463.13 ± 1.25 to 503.73 ± 11.20 μm, P < 0.05). However, the interlamellar distance (from 39.53 ± 0.98 to 34.67 ± 1.0 μm, P < 0.05) and the effective gas exchange area (from 90.23 ± 0.72 to 87.60 ± 2.04%, P < 0.05) were reduced under heat stress. The lamellar clubbing, epithelial hyperplasia, and epitheliocystis were also observed in the gills. Thermal stress significantly increased serum aspartate aminotransferase (from 37.32 ± 1.22 to 50.40 ± 1.18 U/g prot, P < 0.05) and alanine aminotransferase (from 40.27 ± 1.43 to 62.07 ± 1.40 U/g prot, P < 0.05) activities, along with malondialdehyde content (from 8.93 ± 0.46 to 24.64 ± 2.49 nmol/mg prot, P < 0.05) and superoxide dismutase (from 308.67 ± 8.23 to 392.82 ± 9.07 U/mg prot, P < 0.05), catalase (from 2.81 ± 0.06 to 4.14 ± 0.25 U/mg prot, P < 0.05) and glutathione peroxidase (from 10.44 ± 0.10 to 13.23 ± 0.24 U/mg prot, P < 0.05) activities. The expression levels of hsp70 (2.41-fold, P < 0.05), hsp90 (2.72-fold, P < 0.05), p53 (10.15-fold, P < 0.05), bax (4.22-fold, P < 0.05) and caspase-3 (7.21-fold, P < 0.05) were significantly upregulated under heat stress, whereas bcl-2 (0.56-fold, P < 0.05) was downregulated. Moreover, the percentage of apoptotic cells increased significantly in the heat-stressed group compared to the control group (from 0.96 ± 0.17% to 6.29 ± 0.23%, P < 0.05). These results elucidated the mechanistic cascade of heat-induced multi‑tissue damage in black rockfish, integrating oxidative stress, gene expression, and p53‑mediated apoptosis, which offered physiological benchmarks for assessing climate vulnerability in black rockfish.