The present study was designed to investigate the acute sublethal toxic effects of nonylphenol in the south Indian cichlid fish, Pseudetroplus maculatus. The fish was exposed to sublethal concentrations of nonylphenol (89 and 178 μg/ L) for 24, 72 and 96 h durations. The effects of nonylphenol on the rate of oxygen consumption, haematological and histopathological parameters were evaluated. Nonylphenol treatment at both sublethal concentrations caused significant increase in the rate of oxygen consumption up to 48 h, followed by a decrease after 72 h when compared to the control groups. Haematological parameters such as erythrocyte count were decreased whereas total leukocyte count increased significantly in concentration and time-dependant manner. Nonylphenol exposure altered normal architecture of gill as revealed by curling and destruction of secondary lamellae, aneurysm and hyperplasia in gill arches. Hepatic cells showed cytoplasmic vacuolization, degeneration of hepatocytes and severe necrosis. The present study revealed that nonylphenol caused alterations in oxygen consumption and haematological parameters along with degenerative changes in various vital organs thereby proving non-estrogenic adverse effects, which possibly disturb general health condition of fish in natural population.