Stabilization of the blood salt regulation occurred in most of 

 the test conditions within six hours after transfer. At 18°C steady 

 states occurred in 10, 15, 25, and 36°/ooS after six hours and in 2 

 and 5°/ooS after four days. At 25°C new steady -state osmotic levels 

 appeared in all salinities except 5°/oo within one day. In salinities 

 below 15°/ooS, considerable individual fluctuations (Ref. the standard 

 deviation values) were seen in the regulation process. On the basis 

 of the actual mean values it was hard to decide whether the animals 

 attained new steady-state levels within seven days. But the moving 

 averages indicate the possibility of complete acclimation to these 

 media. At 32°C steady-state levels did not appear within one week 

 in 2 and 36°/ooS. Steady-state levels were reached in other salin- 

 ities within a day. In 2°/ooS greater fluctuations continued in the 

 regulation of individual shrimp for six hours after the transfer. 

 There was also a high mortality in 2°/ooS. 



Time Course of Blood Ion Regulation 



Regulation of inorganic blood ions was followed in Penaeus aztecus 

 during the time course of salinity and temperature adaptation. Among 

 the ions analyzed were blood chloride, calcium, magnesium, and potas- 

 sium. 



Effect of 25°C acclimation on chloride regulation 



The chloride ion regulation of shrimp acclimated in 15°/ooS and 

 25°C was studied in the time course of salinity adaptation at test 

 temperatures 25°C (Fig. 13), 32°C (Fig. 14), and 18°C (Fig. 15). 



The shrimp acclimated to and tested in 25 °C experienced an initial 

 rapid chloride ion exchange in 5 and 25°/ooS for about an hour or two. 

 In 2 and 36°/ooS the ion exchange continued for nearly six hours. 

 The high standard deviation values in 2 and 36°/ooS indicated the 

 large regulatory fluctuations between individual shrimp. In 32° and 

 18°C the initial salinity-related response pattern was similar as in 



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