AMMONIA EXCRETION IN PENAEUS-MONODON POSTLARVAE DURING HANDLING AND TRANSFER

The ammonia excretion rate was used as an index of the physiological s tate of Penaeus monodon postlarvae (PL) by monitoring excretion rates after handling and transfer to physiologically different media. The am monia excretion rate of postlarval P. monodon increased from a mean of 0.543 mug to 0.815 mug total NH3-N per mg dry wt per hour after trans fer from 32 to 20 ppt sea water. PL transferred to 40 ppt showed a sig nificant decrease in excretion rate to 0.423 pg total NH3-N per mg dry wt per hour. These changes in excretion rate after transfer to differ ent salinities were only temporary since acclimatized PL showed only m inor deviations in excretion rate from the control. PL transferred fro m normal (8.2) to low (7.2) pH had elevated ammonia excretion rates, f rom 0.591 mug to 0.733 mug total NH3-N per mg dry wt per hour, while t hose transferred to high pH (9.2) had excretion rates that dropped dra stically to 0.259 mug. About 40% of the PL in high pH were moribund af ter the 150 min exposure. The ammonia excretion rate of PL after a 1 h our feeding was twice that of unfed PL during the first 15 min after t ransfer. This difference narrowed with time and was no longer signific ant at 75 min after transfer which was also the duration that represen ted the postprandial surge in ammonia excretion after the 1 hour feedi ng.