However, these ions play a very important role in certain physiolog- 

 ical processes and therefore the study of their regulation is im- 

 portant. These ions like the others exhibited the three acclimation 

 phases--immediate response, stabilization, and new steady state. 



Calcium ion regulation 



Shrimp acclimated to and tested at 25 °C exhibited the initial 

 shock effect from one or two hours in 5, 10, and 25°/ooS (Fig. 22). 

 In 32°C (Fig. 23) and 18°C (Fig. 24) test conditions the effect con- 

 tinued from two to four hours in 5, 10, and 15°/ooS and longer in 2 

 and 36°/ooS. Between 18° and 32°C the animals experienced a pro- 

 longed shock effect at 18°C. Also at this temperature the initial 

 calcium loss in salinities 15°/oo and below was relatively high. 

 The salts were, however, partly retrieved later during stabilization. 



Stabilization of calcium ion regulation in shrimp acclimated to 

 25°C (Fig, 22) started on the first day in nearly all test conditions, 

 although it was less effective in 2 and 36°/ooS. Large fluctuations 

 occurred in both 25 and 36°/ooS at the three temperatures. At 32 °C 

 fluctuations were also present in low salinities. 



The large standard deviation values indicate variations in in- 

 dividual regulation. These variations were more pronounced in 2 and 

 36°/ooS than in other salinities. TemperatUrewise, the variations 

 were not as large in 18°C as in 25° and 32°C. Steady states were 

 attained in 5, 10, 15, and 25°/ooS within a week. At 18°C a steady 

 state was observed in 2°/ooS but not in the control salinity. Gen- 

 erally the survival rates were good in all conditions. 



Blood calcium ion regulation of shrimp acclimated to 18°C was 

 determined in 18°C (Fig. 25), 25°C (Fig. 26), and 32°C (Fig. 27). 

 The control mean calcium level in these animals was higher than in 

 25° or 32°C conditions. There was a sudden initial drop in the 



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