Comparative analysis of serum and skin mucus biochemicals of Labeo catla (Hamilton, 1822) fingerlings in response to acute copper sulphate exposure stress

The present study investigated stress biomarkers in the skin mucus and serum of Labeo catla fingerlings following chemical stress exposure. Fish were subjected to a sub-lethal concentration of copper sulphate (CuSO 4 ) (0.17 mgL − 1 ), equivalent to 50% of the 96 h LC 50 value (0.34 mgL − 1 ), for six hours to evaluate the potential of mucus biochemicals as non-invasive indicators of stress. After exposure, fish were maintained under controlled conditions, and samples of mucus and serum were collected from non-stressed fish (control) and stressed fish at different time intervals: 0 h, 1 h, 3 h, 6 h, 12 h, 24 h, and 48 h post-stress. Biochemical stress parameters, including glucose, total protein, albumin, globulin, albumin to globulin ratio (A: G ratio), triglycerides, cholesterol, total bilirubin, direct bilirubin, creatinine, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), superoxide dismutase (SOD), catalase (CAT), cortisol, lysozyme, heat shock protein 70 (HSP-70), Immunoglobulin M (IgM), were quantified in both mucus and serum. Pearson’s correlation analysis revealed strong positive correlations between serum and mucus parameters, except for the A: G ratio, indicating that mucus reliably reflects systemic stress responses. Principal component analysis (PCA) of the mucus data further identified ALT, SOD, CAT, lysozyme, IgM, and albumin as key mucus biomarkers responsive to acute CuSO 4 exposure. These findings demonstrate the potential of epidermal mucus as a robust, non-lethal tool for fish health assessment, with important implications for aquaculture management and environmental toxicology.