Physiological Responses and Post-Exposure Recovery of the Hepatopancreas in Nile Tilapia Following Copper Exposure

Copper is a common pollutant in aquatic environments. Excess copper in water can enter aquatic organisms through respiration, feeding, and adsorption, thereby exerting serious adverse effects on their health. In this study, NEW Genetically Improved Farmed (GIFT) Nile tilapia (Oreochromis niloticus L.) was used to explore the effect of copper on the hepatopancreas and post-exposure recovery. Acute exposure was simulated via an intraperitoneal injection of 3.75 mg Cu2+/kg body mass, while physiological saline injections served as the control. Samples were collected on days 1, 7, 14, and 21 post-exposure to evaluate growth performance, histopathological changes, antioxidant enzyme activities, and the expression of oxidative stress-related genes in the hepatopancreas. The results show that body length and mass increased within 21 days of the injection and copper exposure did not significantly affect fish growth. On day 1 after copper injection, numerous vacuoles appeared in hepatopancreatic tissues. On day 14, congestion and obvious hepatic sinusoids were observed. However, on day 21, the tissue structure showed gradually recovery. Compared to the control group, superoxide dismutase (SOD) activity was significantly higher in the exposed group on days 1, 14, and 21, and SOD gene expression was significantly elevated on day 21. Catalase (CAT) activity was significantly higher on day 7, and the expression of the CAT gene increased significantly on days 1 and 21. Glutathione peroxidase (GSH-Px) activity decreased significantly on day 7, whereas GPX gene expression increased significantly at the same time point. No significant difference in acetylcholinesterase (AChE) activity was observed during the experiment. In conclusion, copper administered via intraperitoneal injections induced significant activation of the antioxidant defense system and histopathological damage in the hepatopancreas of tilapia. Although tissue damage gradually recovered over time, the activation of the antioxidant defense system partially persisted. Ultimately, copper exposure did not significantly affect growth indicators such as body length and mass. These results advance our understanding of copper toxicity in farmed fish and provide a scientific reference for safe aquaculture production.