Female Oreochromis niloticus were exposed to 1/10 LC50 (0.21ppm) of butachlor herbicide for 6 weeks. Weekly specimens were taken for fecundity estimation. Also hormonal and enzymatic levels were determined in addition histopathological alterations in ovaries and liver were detected. Butachlor exerted drastic effects on absolute and relative fecundity. Sex hormones (testosterone "T" and estradiol "E2") dropped significantly. The high significantly decline in Total Ripen Egg Number was assisted by the coagulative necrosis and oocytic atrasia in ovaries. In addition, thrombus formation and hepatoadenocarcinoma were pronounced in the liver and resulted in the significant drop in ALT and total protein levels. So, it is recommended to apply the biological control of pests in substitution to herbicids in rice fields.