not exhibit the normal appetite. Therefore, starvation was an unlikely 

 factor for the low oxygen uptake at 32°C in 2, 5, and 36°/ooS. On the 

 other hand, this appears to be a case where the shrimp failed to re- 

 spond to temperature rise. Animals acclimated to 18° and 32°C and 

 tested in 25° and 32 °C conditions, exhibited more or less the same 

 trend. 



Regulation of Other Cations 



The results have shown that magnesium regulation was consistently 

 hyposmotic and calcium regulation hyperosmotic to the test salinities. 

 Magnesium concentration changed relatively less in salinities below 

 the control as did the calcium and potassium. In 25 and 36°/ooS 

 magnesium increased considerably in animals acclimated to 25°C and 

 tested in 18°, 25°, and 32°C. Similar increases were also found in 

 shrimp acclimated to 32°C and tested in 25° and 32°C. The ion in- 

 crease was much less in animals acclimated to 18°C and tested at 18°, 

 25°, and 32°C as well as in those acclimated and tested at 32° and 

 18°C, respectively. 



In 25 and 36°/ooS calcium increased uniformly regardless of 

 acclimation or test temperatures. Animals acclimated to 25° and 

 32°C exhibited slightly higher ion concentrations at 32°C than in 

 other test temperatures. 



Potassium was hyperosmotic below the 25°/ooS level at 18° and 

 25°C, without regard to the acclimation temperature. At 32°C test 

 temperature the ion was hyperosmotic to the entire test salinity 

 range in shrimp other than those acclimated to 18°C. 



In Penaeus aztecus and P^. setiferus , McFarland and Lee (1963) 

 observed muscle calcium and magnesium at fairly constant levels in 

 brackish water and seawater; but potassium increased with salinity. 



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