The current study estimates the impact of different common herbicides on antioxidant defenses and histological 
structure of liver and spinal cord of juvenile tilapia. Eighty-four fish were divided into seven groups: group 1 fish 
acted as controls and the remaining fish were exposed to sublethal concentrations of acetochlor, bispyribac- 
sodium, bentazon, bensulfuron-methyl, halosulfuron-methyl, or quinclorac at sublethal concentrations 2.625, 
0.800, 36.00, 2.50, 1.275, and 11.250 mg/l, respectively, for 96 h. Antioxidant parameters changed in response 
to some test herbicides and the greatest effects were caused by exposure to acetochlor and quinelorac for all 
antioxidant measurements. Prominent histological changes in liver tissue included loss of liver architecture and 
the appearance of fatty liver cells, necrotic areas, foci of leukocytic infiltration and many apoptotic cells. The 
most obvious changes in the spinal cord in all treated fish were degradation of myelinated white matter fibers 
with the emergence of empty spaces, large aggregation of pyknotic neuroglial nuclei, and damaged areas in the 
dorsal horn of gray matter. Collectively, the harmful effect of tested herbicides on antioxidant capacity and 
significant alterations in histological structures of liver and spinal cord of Oreochromis niloticus.

Keywords: Nile tilapia; Antioxidant activity; Liver; Spinal cord; Histological structure