Effect of different concentration of cypermethrin on various histological structure of Brian of Schizothorax esocinus. (A) Control showing normal fish brain having no discolouration, no lesions, no morphological changes and have normal hippocampus. (B) fish exposed to 1 ppb showing (P) Pyknosis and (DC) Degenerative changes. (C) fish exposed to 2 ppb showing (P) Pyknosis, (N) Necrosis and (BC) Blood congestion. (D) fish exposed to 3 ppb showing (BC) Blood congestion, (N) Necrosis and (P) Pyknosis. (E) fish exposed to 4 ppb showing (BC) Blood congestion, (N) Necrosis and (P) Pyknosis.