<p>This study investigates the impact of copper sulfate (CuSO₄) on goldfish (<i>Carassius auratus</i>), focusing on histological changes in gills, liver, and muscle tissues, as well as the expression patterns of key genes involved in muscle. Goldfish were exposed to three concentrations of CuSO₄ (1.998 mg/L, 3.995 mg/L, and 5.993 mg/L) for 96 h. Histological examination revealed dose-dependent pathological changes, including gill epithelial proliferation, hepatocyte degeneration, and muscle necrosis. Gene expression analyses indicated significant upregulation of IGF-1 in the liver at high CuSO₄ concentrations, while IGF-1 in muscle was consistently downregulated across all concentrations. MyoD gene expression was upregulated at the three tested concentrations, but it was the lowest at the highest concentration, whereas MURF2 was significantly upregulated in all experimental groups. These findings suggest that CuSO₄ exposure disrupts normal histological structure in goldfish, highlighting the need for stringent environmental regulations to mitigate copper pollution in aquatic ecosystems. This study provides critical insights into the molecular and histopathological mechanisms underlying CuSO₄ toxicity in fish, contributing to the development of evidence-based management strategies for aquatic conservation and aquaculture.</p> Graphical Abstract <p></p>