Intermolt to premolt males of Hemigrapsus takanoi were exposed to salinities of 0, 10, 20 (control), 30, and 40 ppt. After 2, 4, and 6 h of exposure, oxygen consumption and ammonia excretion were measured. Hemolymph osmolality was measured at the end of 8 h. No mortalities were observed until hemolymph sampling. Hemolymph osmolality was maintained between 570 to 840 mmol/kg. Oxygen consumption increased significantly only at 0 ppt, compared to the control (20 ppt). Ammonia excretion levels showed a remarkable increase at 0 ppt. These results indicate that this species expends increased metabolic effort to tolerate abrupt salinity changes to freshwater compared to brackish or seawater.