Effect of ammonia on respiratory functions of blood of Tilapia zilli

The present paper attempts an examination of different changes of blood respiratory properties when Tilapia zilli is exposed to ammonia in three sublethal concentrations (1.1, 2.2 and 3.3 mg NH₃ l⁻¹) for 2 weeks. The results revealed that oxygen and carbon dioxide partial pressures (P_O2 and P_CO2) were changed differently and irregularly both in the caudal artery and in the heart. The acid–base status (pH, HCO⁻₃, TCO₂ and base excess) of arterial and venous blood changed towards alkalosis during the first week. These changes were exaggerated during the second week of ammonia exposure. O₂ saturation of arterial blood was decreased, while that of venous blood was increased due to the disturbances in blood gas transport and exchange mechanisms and in the acid–base status. The oxygen equilibrium curve was shifted to the left and P₅₀ was decreased during most of the experimental periods.