highest ion concentration of all temperatures in 10°/ooS and above. 

 The regulatory pattern between 18° and 25 °C test temperatures was 

 very similar to each other. 



The shrimp acclimated to 18°C failed to show any trend that can 

 be related to temperature. The animals tested at 18°C showed varia- 

 tions from those in 25°C, as much as the latter group differed from 

 the 32°C test animals. However, at 18°C the calcium ion regulation 

 appeared to be more effective in the range of 5 to 36°/ooS. In shrimp 

 acclimated to 32°C and tested at 18° and 25°C similar efficiency was 

 confined to a narrower range of 5 to 25°/ooS. 



Magnesium regulation 



Blood magnesium increased with test salinities. But the ion 

 levels were consistently hyposmotic to the isosmotic line (Fig. 83). 

 In the range of 2 to 15°/ooS the ions did not increase in proportion 

 with the salinities while in 25 and 36°/ooS the blood magnesium con- 

 centration increased out of proportion. The animals acclimated to 

 18°C were, however, an exception to this increase as were those ac- 

 climated to 32°C and tested in 18°C. 



The shrimp acclimated to 25 °C did not show great temperature 

 related variations when tested at 18°, 25°, and 32°C in the respective 

 test salinities. On the other hand, the shrimp acclimated to 32°C 

 were more temperature sensitive than the others. Magnesium ion con- 

 centration in 25 and 36°/ooS increased so much that the concentra- 

 tion levels became almost parallel to the isosmotic line in test tem- 

 peratures 25° and 32 °C. Many of the motile and active organisms are 

 known to attempt to exclude excess magnesium above certain concen- 

 trations. The failure to get rid of the high concentration of mag- 

 nesium in brown shrimp would suggest the possible impairment of ion 

 regulation in 25 and 36°/ooS at 25° and 32°C combinations. The ions 

 were at the same time better regulated in 25 and 36°/ooS when tested 

 at 18°C. 



157 



