Fishes are largely used for the assessment of aquatic environmental quality and are accepted as bioindicators of environmental pollution. Studies of hematology provide useful information on the effects of the external environment on the internal physiology of fish. This present study aims to evaluate the variation in blood parameters of Clarias buthupogon and Heterobranchus longifilis. Different hematological and biochemical indices like red blood corpuscles (RBC), white blood corpuscles (WBC), haemoglobin (Hb %), haematocrite (PCV) and erythrocyte indices like mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), total protein, glucose, cholesterol, albumin, chloride, hydrogen carbonate, potassium, sodium and calcium were determined using standard laboratory procedures. Generally, haematological indices were significantly (p<0.05) low in the dry season as compared to rainy season. Plasma protein was low in the dry season (4.56±1.45 g/dl) and slightly high during rainy season (11.12±19.72 g/dl) and downstream A (3.73±1.37 g/dl) to downstream B (11.94±19.40 g/dl). Glucose level was high at downstream A (156±12.12 g/dl) and in the dry season (150.94±12.53 g/dl), while there was no significant correlation between the value of albumin (p<0.05) but there were significant correlations (p<0.05) for other biochemical indices for both sampling sites and seasons. Observation of blood parameters allows the most rapid detection of changes in fish after the exposure to xenobiotics. It can be concluded that hematological and biochemical parameters could be ranked as possible biomarkers of pollution.

Key words: Toxic effects, pollution, bioindicator, aquatic and Asa River.