Oxygen uptake (O 2 , mg g - 1 h - 1 ) and ammonia-N excretion (ANE, μg g - 1 h - 1 ) of Penaeus japonicus juveniles (0.28 ± 0.04 g), which had been exposed individually to control (0), 1, 5, 10 and 20 mg I - 1 saponin for one day at seawater of 18, 26 and 34 practical salinity units (psu), were measured after depuration for 6 h in clean seawater at each salinity level. Both oxygen uptake and ammonia-N excretion of shrimps increased with decreasing salinity, and increased directly with previous saponin concentration. P. japonicus, which had been previously exposed to saponin as high as 20 mg l - 1 for 24 h, was considered to increase its respiration rate and metabolism during 6 h depuration process.