the shrimp in 18°C failed to stabilize the blood osmoconcentration 

 in some of the salinities for a whole day. 



Stabilization and new steady-state levels seemed to have occurred 

 in 32°C within the first day in 10, 15, and 25°/ooS. The new steady- 

 state levels were also maintained at relatively higher levels than in 

 shrimp from 25°C acclimation temperature. In 2, 5, and 36°/ooS the 

 process of stabilization was still in progress at the end of the ex- 

 periments. 



In test temperatures 25° and 18°C stabilization in osmoregulation 

 and new steady states were attained in 10, 15, and 25°/ooS. The steady- 

 state levels decreased gradually with temperature from a highest in 

 32°C. In addition to the above salinities steady-state levels were 

 also established in 2 and 5°/ooS at 25°C but not in 36°/ooS. Al- 

 though the shrimp in IS^C were somewhat successful in controlling the 

 salt loss in 2°/ooS, apparently they failed to reach a steady state. 

 The low sample size in this medium was a result of heavy mortality. 



Effect of 18°C acclimation on osmoregulation 



The osmoregulatory trends of shrimp acclimated to 18°C and 

 tested in 18°, 25°, and 32°C are shown in Figures 10 to 12. The 

 mean control osmoconcentration values of 18°C acclimated shrimp 

 were the highest (674 mOsm) of all test temperatures (Fig- 10)- 

 As in the previous two groups there was a steep loss or gain of 

 salts following the transfer to various salinities at 18°C. The 

 duration of salt exchange between the shrimp and the external media 

 increased with the deviation of test salinities from 15°/ooS. Tlie 

 salt exchange occurred for less than two hours in salinities close 

 to control while in 36°/ooS it continued for a maximum of ten hours. 

 The initial osmoregulatory pattern at 25°C (Fig. 11) and 32°C (Fig. 

 12) remained essentially the same as in 18°C except that in 5 and 

 10°/ooS the animals continued to lose the blood salts longer than 

 in other concentrations. 



68 



