Abstract
<title>Abstract</title> <p>Microcystin-LR (MC-LR) is one of the most prevalent cyanobacterial toxins in freshwater ecosystems and poses a significant threat to aquatic organisms through chronic dietary exposure. Although the toxic effects of MC-LR have been widely documented, its integrated impacts on oxidative stress, stress physiology, and immune modulation remain poorly understood. In the present study, crucian carp were exposed to diets containing 0, 50, 100, 200, and 400 µg/kg MC-LR for 4 weeks to evaluate physiological, oxidative, and immunological responses. Dietary MC-LR exposure significantly reduced body weight gain, feed efficiency ratio, and specific growth rate, while increasing the hepatosomatic index. Red blood cell count, hemoglobin, and hematocrit decreased in a concentration-dependent manner, indicating hematological impairment. Plasma glucose, aspartate aminotransferase, and alanine aminotransferase increased, whereas total protein decreased, reflecting metabolic disturbance and hepatocellular damage. Antioxidant responses were characterized by elevated superoxide dismutase and catalase activities, particularly in the liver, suggesting activation of compensatory defenses against oxidative stress. Cortisol and heat shock protein 70 levels increased significantly following MC-LR exposure, demonstrating sustained physiological stress. Furthermore, TNF-α, IL-1β, TGF-β, and IL-10 were differentially regulated in the spleen, head kidney, and liver, indicating organ-specific immune modulation. Integrated biomarker response analysis revealed progressive increases in overall biological disturbance with increasing concentration and exposure duration. These findings demonstrate that chronic dietary MC-LR exposure induces coordinated oxidative, physiological, and immunological disturbances in crucian carp, linking redox imbalance with stress activation and cytokine-mediated immune responses. The present study identifies biologically relevant biomarkers for assessing chronic cyanotoxin toxicity in freshwater fish</p>