Aim: Since 1940s, chemical pesticides of one form or another have become a dominant and essential form of pest control throughout much of the world. Because of the widespread use of pesticides for domestic and industrial applications, the evaluation of their toxic effects is of major concern to public health. The aim of the present study was to investigate the toxicogenomics effects of dimethoate (DM), an organophosphorus pesticide, to target the chromosomes of fish. Methodology: In the present investigation, two species of Cyprinuscarpio L. i.e. Cyprinuscarpiospecularis and Cyprinuscarpiocommunis were treated with three sub-lethal concentrations of DM (5 ppm, 10 ppm, __ampersandsignamp; 15 ppm.). After treatment, the frequency of micronuclei was examined at the duration of 24, 48 and 72h. The micronucleus test (MNT) was used for assessing the genotoxicity of the fishes by the preparation of slides and scoring of micronuclei. Results: The pesticide treatment caused significant changes in the frequencies of micronuclei in erythrocytes of Cyprinuscarpiospecularis and Cyprinuscarpiocommunis. Micronuclei were non-refractive small nuclei lying near the main nucleus displaying the same pattern as the main nucleus. Nuclear abnormalities were like cells with binuclei, blebbed nuclei, lobed nuclei and notched nuclei. Conclusion: It was concluded that the pesticide dimethoate possess mutagenic potential at varying extent. A time and dose dependent increase in the frequency of micro-nucleated erythrocytes was found.