An in vivo study on the genotoxic effects of pentachlorophenol (PCP) and 2,4-dichlorophenoxyacetic acid (2,4-D) was carried out with freshwater air-breathing fish Channa punctatus. The fish were exposed to three sublethal doses of PCP (0.2, 0.4, and 0.6 ppm) and 2,4-D (25, 50, and 75 ppm) by medium treatment. Micronucleated erythrocytes were sampled at intervals of 48, 72, and 96 h post-treatment. Student's t test revealed significant increases in micronucleus (MN) frequency. Maximum incidence of MN was recorded at highest concentrations and durations for both chemicals. A time- and dose-dependent response of the MN frequency for both chemicals was confirmed. PCP-treated groups had 8-10 MN per cell, specifically at higher concentrations and duration. Echinocytes were recorded at higher concentrations of 2,4-D. The study confirmed the genotoxicity of PCP and 2,4-D in this organism. PCP was found to be more toxic than 2,4-D in terms of MN induction. This assay has further potential for detecting genotoxic compounds in aquatic ecosystems.