Molecular and Physiological Insights Into Handling Stress Responses in Hybrid Grouper (Epinephelus fuscoguttatus × Epinephelus lanceolatus)

Handling stress is a significant challenge in intensive aquaculture, often compromising fish welfare, immunity, and overall productivity. This study investigates the skin transcriptomic responses, blood plasma enzyme activities, and histological changes in the liver, spleen, and head kidney of hybrid grouper (Epinephelus fuscoguttatus × E. lanceolatus) subjected to repeated handling stress over 10 consecutive days. RNA-sequencing of the skin identified 2521 differentially expressed genes (DEGs), showing significant enrichment in oxidative phosphorylation and cardiac muscle contraction pathways. Stress conditions upregulated genes such as NADH ubiquinone oxidoreductase, ATP synthase, cytochrome b-c1 complex, cytochrome c oxidase, succinate dehydrogenase complex subunit B, and troponin T2d cardiac, indicating enhanced mitochondrial activity and energy turnover. These molecular signatures correlated with physiological recovery in stress-resilient (handling-resilient [HR]) fish, as evidenced by elevated alanine transaminase levels and preserved hepatic morphology. In contrast, stress-sensitive (handling-sensitive [HS]) fish exhibited a pronounced reduction in hepatic cytoplasmic area (48.75 ± 0.47 μm2) compared to the control (62.47 ± 0.20 μm2) and HR (67.82 ± 0.24 μm2) groups. Furthermore, HS fish showed severe splenic necrosis (3.15 ± 0.68 μm2) compared to the control (0.27 ± 0.29 μm2), reflecting impaired metabolic and antioxidant capacity. This integrated analysis elucidates the molecular and physiological impacts of handling stress and identifies key pathways linked to stress resilience. Implementing refined handling techniques is essential to mitigate stress-related health impacts and enhance welfare in hybrid grouper aquaculture.

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