as they did when tested in 32°C. At 18°C test conditions the concen- 

 tration levels were relatively high over the entire salinity range 

 particularly in low salinities. In 25 and 36°/ooS the high levels 

 were attained two or three days after transfer. In 2, 5, and 

 10°/ooS the shrimp tested at 25° and 18°C showed similar regula- 

 tory patterns as they also did in 25 and 36°/ooS when tested in 

 25° and 32°C. 



The shrimp acclimated to 32 °C and tested in other temperatures 

 showed some important changes in the ionic regulation (Fig. 95) . At 

 18°C the shrimp failed to maintain the same concentration levels as 

 the animals did when acclimated to 25°C and tested in 18°C (Fig. 94). 

 The concentrations in 2, 5, 10, and 15°/ooS reached the lowest levels, 

 from the initial high levels, within the first day. In 25 and 36°/ooS 

 the concentrations at 18°C were consistently low. In contrast, the 

 shrimp tested in 25°C maintained higher final levels in most of the 

 salinities. In general, responses in magnesium ion regulation of 

 shrimp tested in 32° and 25°C were similar in most of the salinities. 



The animals acclimated to 18°C (Fig. 96) exhibited a response 

 pattern in low salinities much the same as those acclimated to 25°C 

 and tested in 18°, 25°, and 32°C (Fig. 94). Highest magnesium con- 

 centration levels were found in 2, 5, and 10°/ooS when tested in 

 18°C. Actually, at 18°C the magnesium regulation was quite effi- 

 cient in all salinities. At 25° and 32°C the ion concentration 

 levels were relatively low during the first or second day after 

 transfer. 



Potassium ion 



Blood potassium ion regulation exhibited a definite temperature- 

 related pattern in the various salinities unlike magnesium ion. Po- 

 tassium ion regulation of brown shrimp acclimated to 25°C and tested 

 in 18°, 25°, and 32°C is shown in Fig. 97. The ion concentration 



174 



