calcium ion concentration in all the test conditions. Stabilization 

 of calcium ion regulation started on the first day in all temperatures. 

 New steady-state levels appeared within the test period in 18°C in all 

 salinities except 25°/ooS, a medium which was close to the control sa- 

 linity. By the time the tests were concluded, the process of stabili- 

 zation was still in progress in most of the salinities at 25° and 32°C 

 except in some of the dilute media. A steady-state level was not 

 reached even in the control salinity 15°/oo in 25° or 32°C. Also the 

 regulatory fluctuations were large at 25° and 32°C, both among indi- 

 vidual shrimp and between sampling intervals. 



Brown shrimp acclimated to and tested at 32°C showed relatively 

 fewer variations in their initial regulatory responses (Fig. 28). 

 But more variations were present when tested at 25° or 18°C (Figs. 

 29 and 30, respectively). Even though stabilization started within 

 a few hours, new steady states were attained in only some of the 

 conditions. At 32°C, which was their acclimation temperature, 

 steady-state levels appeared in none of the salinities. At 18°C 

 steady-state levels appeared in all salinities except 2°/ooS while 

 at 25°C the levels appeared in 5, 10, and 15°/ooS. The low sample 

 size in 2°/ooS after 16 hours was a result of the high mortality 

 rate. 



Magnesium ion regulation 



Brown shrimp acclimated to 25°C were tested at 25°C (Fig. 31), 

 32°C (Fig. 32), and 18°C (Fig. 33). The control mean (15°/ooS and 

 25 °C) of magnesium ion concentration was higher at 25 °C than at the 

 other acclimation temperatures. There was a sudden initial increase 

 in the magnesium ion concentration in all the test salinities ex- 

 cept 2°/ooS (Fig. 31). Within two hours the ion concentration began 

 to decrease in 2, 5, and 10°/ooS. A similar pattern was seen at 

 32°C (Fig. 32). Magnesium ion regulation appeared to be more effi- 

 cient at 18°C (Fig. 33), particularly in the dilute media. The regu- 

 latory efficiency of shrimp acclimated to 25 °C decreased in 25 and 



88 



