Saline-alkaline water resources are widely distributed in China. However, their imbalanced ionic composition, high pH, and elevated carbonate alkalinity significantly impair normal growth and reproduction of fish. Although previous studies have explored the effects of saline-alkaline stress on the growth performance of aquatic organisms, these investigations have largely focused on low-concentration environments, leaving the impacts of high-concentration conditions on growth performance and associated metabolic changes insufficiently understood. This study aimed to elucidate the mechanisms by which carbonate-alkaline environments affect the growth performance and physiological metabolism of crucian carp (Carassius auratus). Experimental fish were randomly assigned to three groups: a freshwater control group (Con), a 20 mmol/L NaHCO3 exposure group (T), and a 40 mmol/L NaHCO3 exposure group (F), subjected to carbonate-alkaline exposure for 56 days. Through the application of growth indices, biochemical assays, and non-targeted metabolomics analysis using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) coupled with multivariate techniques such as principal component analysis (PCA), orthogonal partial least squares-discriminant analysis (OPLS-DA), and pathway enrichment tools like MetaboAnalyst 5.0 and KEGG database, the study systematically examined the effects of carbonate-alkaline exposure on the growth, oxidative defense, and metabolomics profile of crucian carp. The results revealed that carbonate-alkaline exposure significantly suppressed growth indices, including weight gain rate, specific growth rate, and feed conversion efficiency. Moreover, with increasing carbonate-alkaline concentrations, antioxidant enzyme activities in the liver—such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px)—and blood biochemical parameters, including blood ammonia, blood urea nitrogen (BUN), total cholesterol (TC), and triglycerides (TG), underwent notable alterations. Pathway enrichment analysis identified 17 statistically significant differential metabolites (DEMs) in the Con vs. T group, enriched in 27 metabolic pathways, including unsaturated fatty acid biosynthesis, purine metabolism, glycerophospholipid metabolism, and glutathione metabolism. In contrast, the Con vs. F group identified 100 DEMs enriched in 35 pathways, encompassing additional processes such as arginine biosynthesis, starch and sucrose metabolism, glyoxylate and dicarboxylate metabolism, arachidonic acid metabolism, and sphingolipid metabolism. The findings indicate that carbonate-alkaline exposure imposes a substantial energetic burden on crucian carp, undermining the energy availability for growth and thereby significantly inhibiting growth rates. This condition induces oxidative stress by disrupting the balance between reactive oxygen species (ROS) and the oxidative defense system, leading to severe hepatic tissue damage. As carbonate-alkaline concentration increases, critical metabolic pathways associated with growth, immune defense, and fatty acid metabolism—such as arginine biosynthesis, unsaturated fatty acid biosynthesis, purine metabolism, glycerophospholipid metabolism, sphingolipid metabolism, and glutathione metabolism—experience pronounced disruption. This exacerbates hepatic damage, compromises immune defense, destabilizes cellular membrane integrity and function, and suppresses cellular proliferation, ultimately impairing normal growth.By integrating growth performance, biochemical analysis, and metabolomics, this study provides a comprehensive understanding of the adverse effects of carbonate-alkaline environments on the growth and hepatic metabolism of crucian carp. The findings offer critical insights for optimizing aquaculture practices involving freshwater bony fish in saline-alkaline waters, contributing to the sustainable utilization of saline-alkaline water resources with significant ecological, economic, and societal benefits.