Nanostructure metal oxides such as tin oxide nanoparticles due to its unique properties have been used as a photocatalyst in semiconductor industries, building optoelectronic devices and numerous other industries. However, the toxicological impact of these SnO₂ nanoparticles is largely yet to be studied, particularly in the aquatic ecosystem. In this direction to evaluate the ecological impact of the SnO₂ nanoparticles on aquatic organisms, selected Catla catla, freshwater fish was selected to examine the hematological and biochemical variations upon treatment with SnO₂ nanoparticles. In the present study LC₅₀ of SnO₂ NPS was found to be 20 mgl-¹observed for 24 h. Further 1/10^th of the LC₅₀ concentration of SnO₂nps (2 mgl-¹) was selected for sublethal investigation for 4-20 days with an interval of 4 days. The results showed alterations in hematological parameters with a decrease in Hemoglobin (Hb), Hematocrit test (Hct %), red blood cells (RBC) and white blood cells (WBC), while there was an increase in mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) values on all days. Further evaluation demonstrated an increase in serum lactate dehydrogenase (LDH), aspartate transaminase (AST) and alanine transaminase (ALT) levels compared to control groups. Studies revealed alterations in oxidative stress markers with a significant reduction in the serum superoxide dismutase (SOD) and catalase (CAT) levels, and an increase in malondialdehyde (MDA) and decrease in gill Na⁺K⁺ATPase concentration. The studies also found increased brain glutamate concentrations indicating possible brain tissue damage. The study highlights the toxicological impact of SnO₂nps and the role of certain potential biomarkers which reflect the impact of the toxicants in the aquatic environment.