This study synthesizes published literature to evaluate how sublethal exposure to Metasystox (oxydemeton-methyl,marketedasMetasystox ®/Metasystox-R)affects haematological indices in freshwater teleosts, with emphasis on Channa punctatus. Organophosphorus pesticides such as oxydemeton-methylactprimarilyvia cholinesterase inhibition and are documented to cause acute and subacute physiological disturbances in fish, including alterations in erythrocyte counts, haemoglobin concentration, hematocrit (PCV), mean corpuscular values, leukocyte profiles and relatedbiomarkersofstressandimmunocompetence. Reported responses are often concentration- and time-dependent, vary among species, and reflect combined impacts of direct erythrotoxicity, oxidative stress, cholinergic overstimulation and secondary metabolic shifts. Based on published experimental data and reviews, characteristic responses in Channa spp. following sublethal Metasystox exposure include decreases in total leukocyte counts and differential changes in WBC subsets, variable RBC and Hb responses (both decreases and compensatory increases reported), and consistent perturbation of PCV and indices (MCV, MCH, MCHC). These alterations have implications for fish health, population viability, and the use of haematological biomarkers in environmental monitoring and risk assessment for organophosphate contamination.