Field-Based Assessment of Hematological, Antioxidant, and Innate Immune Responses in Cultured Mugil cephalus from Ponneri, Tamil Nadu, India

Abstract

   Aquaculture systems are frequently exposed to variations in water quality that can alter the physiological condition, oxidative balance, and immune competence of cultured fish. The present study evaluated hematological, antioxidant, and innate immune responses in juvenile grey mullet (Mugil cephalus) collected from three culture ponds at Pioneer Aquaculture Consultants, Ponneri, Tamil Nadu, India. Fourteen fish were sampled on 5 May 2026, comprising four fish from Pond 1, four from Pond 2, and six from Pond 3. Differential leukocyte profiles, plasma total protein concentration, erythrocyte superoxide dismutase (SOD) and catalase (CAT) activities, and plasma lysozyme activity were determined to assess the integrated physiological response of the fish. Lymphocytes were the predominant leukocyte population in all ponds; however, their proportion decreased from 68.4 ± 4.2% in Pond 1 to 52.6 ± 6.3% in Pond 3, whereas neutrophils increased from 18.2 ± 3.1% to 32.8 ± 4.7%. Total protein concentration declined from 42.8 ± 3.6 to 33.9 ± 3.8 mg/mL. In contrast, antioxidant and innate immune responses increased progressively across the ponds. SOD activity increased from 18.6 ± 2.1 to 31.7 ± 3.4 U/mg protein, CAT activity increased from 12.4 ± 1.5 to 21.6 ± 2.7 U/mg protein, and lysozyme activity increased from 15.8 ± 1.9 to 27.9 ± 3.1 U/mL. Pond 3 therefore exhibited the most pronounced integrated biomarker response, characterized by reduced lymphocyte percentage and total protein concentration and increased neutrophil percentage, SOD, CAT, and lysozyme activities. These findings indicate that the combined assessment of hematological, antioxidant, and innate immune biomarkers can provide a useful early-warning approach for monitoring physiological stress in cultured fish. However, because of the relatively small and unequal sample sizes and the absence of matched pond-specific water-quality measurements for all sampled ponds, the observed relationships should be interpreted as exploratory associations rather than definitive causal effects.