Integrated analysis of physiological indicators and transcriptome in the hepatopancreas of <i>Ruditapes philippinarum</i> under copper stress

To elucidate the toxic effects and adaptive mechanisms of copper stress on Ruditapes philippinarum , and to screen for sensitive biomarkers, this study established a 14-day stress experiment using the 48h median lethal concentration (LC₅₀) of copper as a reference. Two treatment groups were established: 0.0568 mg/L (low concentration, 1/100 of 48h LC50) and 0.568 mg/L (high concentration, 1/10 of 48h LC50). Enzyme activity results showed that LDH, PK, and HK in the clams peaked on Day 2 and then slowly declined, indicating enhanced anaerobic respiration in the early stage of stress; SOD and CAT peaked on Day 7, reflecting the organism’s response to oxidative stress during the middle stage; ACP first dropped to a minimum and then peaked in the middle-to-late stage, marking the activation of immune function in the later stage; TG and TCHO levels both showed a trend of initial decrease followed by an increase, indicating energy consumption for stress response in the early stage and adaptive regulation to maintain membrane function in the later stage; AKP showed no significant regularity. There were significant differences in core response indicators at different stages of copper stress: PK, HK, and LDH responded significantly in the initial stage; SOD and CAT responded strongly in the middle stage, serving as key indicators for the organism to resist oxidative damage; ACP, TCHO, and TG responded significantly in the later stage. Among them, LDH, SOD, ACP, and TG showed stable and prominent responses throughout the stress cycle and can be used as core biomarkers for assessing the toxic effects of copper pollution on Ruditapes philippinarum . Transcriptomic analysis indicated that the number of differentially expressed genes (DEGs) between the high and low concentration groups increased significantly with stress duration, reaching 5,337 (5,088 upregulated, 249 downregulated) on Day 14. GO and KEGG enrichment analyses revealed that the low-concentration group initiated rapid stress responses in material transport and fatty acid metabolism pathways in the early stage, activated antioxidant defense pathways in the middle stage, and coordinated multiple pathways to maintain homeostasis in the later stage. The high-concentration group resisted acute toxicity through lipid metabolism and mitophagy in the early stage, and strengthened detoxification, repair, and metabolic-immune coordinated regulation to adapt to long-term stress in the later stage. This study systematically elucidates the dynamic response patterns of Ruditapes philippinarum to copper stress., providing important physiological and molecular data support for heavy metal pollution monitoring and adaptive mechanism research in marine bivalves.