Abstract: Background and Objective: Atrazine is considered the most common aquatic herbicide used. So, the present study aimed at studying atrazine-induced changes in some biochemical characteristics during early embryonic stages of Clarias gariepinus . These characteristics include two metabolic enzymes, lactate hydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G6PDH), two oxidative enzymes, glutathione reductase (GSH) and superoxide dismutase (SOD), two thyroid hormones, triiodothyronine (T3) and thyroxine (T4), lipid peroxidation (LPO), DNA damage and patterns of protein fractions of different early developmental stages. Material and Methods: Gametes were collected from mature specimens of the African catfish, C. gariepinus from the river Nile. The fertilized eggs were incubated in dechlorinized tap water (pH = 7.7, dissolved oxygen 88-94% saturation, temperature 27-29EC and photoperiod 12:12 (light:dark). Under atrazine influences, different measurements of enzyme activities, electrophoretic protein analysis, lipid peroxidation, DNA fragmentation, Total Protein (TP) and hormones were carried out. Results: The atrazine-induced significant fluctuation in the activity of G6PDH and LDH with a sharp decrease in 24 h-PFS after hatching. There is no significant variations in GSH activity under atrazine doses except in 24 and 96 h-PFS with a decrease in all developmental stages except at 72 h-PFS. Insignificant fluctuation in SOD activity in all developmental stages of C. gariepinus except 4, 20 and 24 h-PFS in comparison to control. Atrazine induced significant fluctuation in DNA damage and LPO/TP ratio in all developmental stages. Insignificant fluctuation in T3 activity but significant decrease in T4 activity in all developmental stages of C. gariepinus under exposure of sublethal doses of atrazine. Conclusion: One could conclude that atrazine significantly disturbe the metabolic parameters of embryonic and developmental stages of fishes and in turn most of these parameters could be used as indicators of environmental aquatic pollution.