The magnesium regulation was apparently very efficient in all 

 salinities in animals acclimated at 18°C. Temperature change to 25° 

 or 32°C did not alter the efficiency significantly as in other ac- 

 climation temperatures. 



Potassium regulation 



Blood potassium increased with the test salinities (Fig. 84) . 

 The ion regulation appeared very efficient in the range of 5 to 

 25''/ooS in shrimp acclimated to 25° and 32°C and tested in 18° and 

 25°C. The ion influx was, however, not effectively checked in 25 

 and 36°/ooS at 32°C. At 18°C potassium was present in the lowest con- 

 centration of all temperatures regardless of the acclimation tem- 

 perature. The ion concentration increased progressively with test 

 temperatures 25° and 32°C. Animals acclimated to 25°C were less 

 sensitive to test temperature variations than those acclimated to 

 18° and 32°C. These shrimp exhibited greater variations with tem- 

 perature. Tlie ion concentration was hyperosmotic to the isosmotic 

 line in salinities of 25"/oo and below. 



Interaction of Salinity and Temperature on Osmotic and Ionic Regulation 



The effect of temperature change on osmotic and ionic regulation 

 was explained on the basis of the responses observed in shrimp accli- 

 mated and tested at 25°, 32°, and 18°C. The control mean blood os- 

 motic or ionic concentration levels represent the values in 15°/ooS 

 in the respective acclimation temperatures. Some references were 

 already made in the previous topics on the impact of temperature on 

 the regulatory process in brown shrimp. However, the major trends 

 of temperature effect will be reported in this section. 



Osmoregulation 



At 25 °C brown shrimp maintained a lowest salt concentration 

 (643 mOsm) in 15°/ooS of all temperatures (Fig. 85). The concentra- 

 tion levels were 657 mOsm at 32°C (Fig. 86) and 674 mOsm at 18°C 



159 



