Sub-lethal acute effects of environmental concentrations of inorganic mercury on hematological and biochemical parameters in walking catfish, Clarias batrachus.

The acute toxicity of mercury to the air-breathing fish Clarias batrachus (Linn.) was determined in this study using hematological (including hemoglobin, hematocrit, total erythrocyte count, total leukocyte count, and mean corpuscular hemoglobin concentration) and biochemical (including total serum protein, serum glucose, triglyceride, cholesterol, albumin) biomarkers at predetermined exposure concentrations (0.069 and 0.139 mg/L). Although significant differences were observed between exposure groups for all hematological and biochemical variables, a distinctive reduction in hemoglobin levels, hematocrit, and total erythrocyte count in the mercury-exposed fish compared to the control was observed from 24 h-96 h. Similarly, marked differences in serum globulin, total serum protein and cholesterol levels were observed across exposure groups from 24 h-96 h. While the marked hematological responses strongly suggestive of toxicant-related anemia, the marked biochemical responses suggest immune-modulation and metabolic disruption. The magnitude of toxic effects under graded toxicant exposures for weighted scores of combined biomarker response index (IBR) indicated an approximately 3-fold deterioration in overall health of mercury-exposed fish compared to control group. Depictions of hematological and biochemical effects in hardy species like Clarias batrachus indicate an imminent onset of anemia, immune-modulation and metabolic disruption within 24hs of exposure to inorganic mercury. Such observations for portends greater deleterious effects to less hardy aquatic biota under acute inorganic mercury environmental exposures.