Oxygen consumption and ammonia-N excretion of Penaeus chinensis juveniles exposed to ambient ammonia at different salinity levels.

1. Oxygen consumption rate (O2 mg/g/hr) and ammonia-N (un-ionized plus ionized ammonia as nitrogen) excretion rate (microgram/g/hr) of Penaeus chinensis juveniles (0.54 +/- 0.11 g) decreased with increase of salinity among 10, 20 and 30 ppt. 2. Oxygen consumption rate increased with increase of ambient ammonia-N at three salinity levels. 3. Ammonia-N excretion rate was highest (204 micrograms/g/hr) in P. chinensis exposed to 0.985 mg/l ammonia-N at 10 ppt, and lowest (-416 micrograms/g/hr) in that exposed to 9.897 mg/l ammonia-N at 30 ppt. 4. In the prawns exposed to 9.921 mg/l ammonia-N at 20 ppt, and to 5.087 and 9.897 mg/l ammonia-N at 30 ppt, ammonia-N excretion was heavily depressed and ammonia-N influx occurred (ammonia-N uptake was much higher than ammonia-N excretion).