Copper-Induced Thyroid Disruption and Oxidative Stress in Schizopygopsis younghusbandi Larvae

In recent years, heavy metal emissions in Lhasa have been increasing, which has an impact on the local water environment. The negative effects of copper (Cu²⁺) on aquatic ecosystems have attracted much attention, as even low concentrations of Cu²⁺ can exert toxic effects on aquatic organisms. However, the impact of Cu²⁺ on native fish species from the Lhasa River remains poorly understood. In this study, <i>Schizopygopsis younghusbandi</i> (<i>S. younghusbandi</i>) larvae were exposed to Cu²⁺ at concentrations of 0. 5, 5, 50, and 500 μg/L for 7 or 14 days to evaluate its toxic effects on thyroid function and the antioxidant system. The results indicate that whole-body total thyroxine (T4) and triiodothyronine (T3) levels were significantly decreased following Cu²⁺ exposure. This decrease was accompanied by a marked increase in <i>dio1</i> and <i>dio2</i> gene expression and decreased expression of thyroid hormone synthesis genes (<i>nis</i>, <i>tg</i>, <i>ttf1</i> and <i>pax8</i>) after exposure to Cu²⁺. Furthermore, the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) and the content of lipid peroxidation were increased, while the content of glutathione (GSH) was decreased. In addition, the survival rates and body lengths of <i>S. younghusbandi</i> larvae were significantly reduced following 7- and 14-day Cu²⁺ exposure. The Integrated Assessment of Biomarker Response (IBR) analysis further revealed dose- and time-dependent effects of Cu²⁺ on the larvae. In conclusion, the findings demonstrate that Cu²⁺ exposure induced disruption of thyroid endocrine and antioxidant systems and caused developmental toxicity in <i>S. younghusbandi</i> larvae.