Toxicity of Agro NPK fertilizer on the histopathology of the African catfish (C. gariepinus) sub adult was investigated in Calabar. The experiment was conducted in triplicates of four treatments. The fish were exposed to concentrations 1.0 g/L, 2.0 g/L, 3.0 g/L and 4.0 g/L. Behavioral changes in fish exposed to different concentrations of Agro NPK fertilizer ranged from erratic swimming, moribund movement, jumping and lack of balance. Similar changes were not observed in the control throughout the experiment. At 1.0g/l concentrations, the mean mortality was 80% with an initial erratic swimming. It was observed that mean mortality increased progressively with increase in concentration of the pollutant (Agro NPK fertilizer). At concentration 3.0 g/L, mean mortality was observed within 72 hours of exposure preceding moribund swimming while the highest mortality was observed at 4.0 g/L.