Evaluation of gonadotropin releasing hormone (GnRH) to physiological changes, spawning and reproductive parameters of African catfish, Clarias gariepinus in the current study has been conducted to determine the effectiveness of GnRH in stimulation the maturation and ovulation of African catfish. GnRH at 4, 8 and 12 μg/kg body weight dissolved in 0.6% NaCl under a natural temperature regime. The fish from Abbasa farm were fed with 30 % protein diet during experiment. Fish550 - 600 g body weight were injected with a doses of (4, 8 and 12 μg/kg body weight) three times a week. Result showed multiple ovulations and spawns within a period of approximately 30 days. Levels of 17β- estradiol (E2), testosterone (T) and follicular stimulating hormone (FSH) were elevated at 30 days' post treatment, preceding the spawns with the highest fecundity. These results show that administration of GnRH induces multiple spawns in fishwhere, approximately 100% increase in red blood cells (RBCs), white blood cells (WBCs), hematocrit value (Hc) and hemoglobin content (Hb) respectively. Also, there are increased in plasma glucose level, total protein, aspartate and alanine amino transferase activities (AST and ALT) and increased in plasma creatinine and uric acid concentration after administration of GnRH. These data suggest that fish respond to administration of GnRH by increasing their hematology, enzymes of liver functions and kidneyfunctions. Injection of GnRH at 4, 8 and 12 µg/kg was found to be effective to induce ovulation in African catfish. 100% ovulation was also observed for the fish treated with GnRH. Also, plasma level of E2, FSH and T increased significantly with the association of ovulation. The present study indicates that administration of GnRH is effective for sexual maturation and ovulation in African catfish.