Toxicity of naphthalene was carried out on Metapenaeus affinis (H. Milne Edward, 1837) to investigate its effects on growth, metabolic index and biochemical constituents. Growth rate in terms of weight gain was 32.13% in control, 12.12% in 0.125 ppm and only 5.22% in 0.25 ppm. Metabolic index assessed in terms of oxygen consumption showed a reduction in respiratory rate up to 44.4% in prawns exposed to naphthalene. Activity increased initially but reduced subsequently. Protein content and organic carbon of the body tissue of juveniles showed reduction on exposure to naphthalene. Inhibitory effect was dose dependent and duration of exposure. However, the lipid content increased after exposure to naphthalene. Changes in the growth and respiratory rate and other biochemical constituents resulting from exposure to naphthalene indicate some adaptive response and recovery during detoxification in the prawns exposed to pollutant. Study revealed that the physiological and biochemical parameters could be used as indicator of stress condition in aquatic organisms and the use of naphthalene should be regulated because of its toxic nature