NITROGEN-EXCRETION AND CHANGES OF HEMOCYANIN, PROTEIN AND FREE AMINO-ACID LEVELS IN THE HEMOLYMPH OF PENAEUS-MONODON EXPOSED TO DIFFERENT CONCENTRATIONS OF AMBIENT AMMONIA-N AT DIFFERENT SALINITY LEVELS

Penaeus monodon (22.064 +/- 2.263 g) were exposed individually at 10, 20 and 30 parts per thousand salinity to 0 (control), 1, 5, 10 and 20 mg l-1 ammonia-N for 24 h. Changes in hemocyanin, protein and free amino acid levels, and whole shrimp ammonia-N excretion, urea-N excretion and dissolved organic N (DON) excretion were determined. Ammonia-N excretion decreased with increased salinity and with increased ambient ammonia-N. Ammonia-N accounted for 56.87, 70.43 and 78.13% of total nitrogen excreted by P. monodon in 30, 20 and 10 parts per thousand, respectively. DON increased to 67.26, 78.79 and 86.1% of total nitrogen excreted by the shrimp exposed to 20 mg l-1 ammonia-N in 30, 20 and 10 parts per thousand, respectively. Net ammonia-N uptake occurred as shrimp were exposed to ambient ammonia-N greater than 5 mg l-1 at all salinity levels tested. Hemocyanin and protein levels decreased, whereas hemolymph ammonia, urea, total free amino acid levels and taurine level increased, with increased ambient ammonia-N. Following exposure to ambient ammonia-N, P. monodon changed its excretory pattern, accumulation of hemolymph ammonia, and catabolism of hemocyanin and protein to balance osmoregulation.