25 °C, but the duration of the immediate response phase was longer. 

 For instance in salinities next to 15°/ooS this response phase con- 

 tinued for about two hours at 32 °C and for about four hours at 18°C 

 as opposed to one hour at 25°C. In 36°/ooS the chloride influx con- 

 tinued for almost ten hours before any stabilization was commenced. 



Stabilization started in most of the salinities at 25° and 32°C 

 test temperatures within ten hours. In 18°C, although major changes 

 occurred from six to ten hours, changes of smaller magnitude contin- 

 ued from 16 to 24 hours. At 25 °C not only was the steady state 

 reached sooner than at 18°C, but the fluctuations in the ionic reg- 

 ulation were minimal. However, at 18°C it should be noted that in 

 2 and 36°/ooS the ion regulation was less steady. In 2°/ooS the 

 shrimp were continuously losing ions to the medium but the rate of 

 loss after the third day was not significant. The ion regulation 

 was unsteady in 36°/ooS. Apparently no steady-state levels appeared 

 in either salinity. 



At 32°C a steady-state chloride level appeared in 25°/ooS slower 

 than in 5, 10, and 15°/ooS. At 18° and 32°C, great ionic regulatory 

 fluctuations were noticed in 2 and 36°/ooS media between the different 

 time intervals (Figs. 14 and 15) and between the individual shrimp. 

 The relatively stable ionic regulation at 25°C indicated that at 

 other temperatures (18° or 32°C) the shrimp were unlikely to handle 

 the chloride regulation problems successfully even after one week 

 particularly in 2 and 36°/ooS. 



Effect of 52°C acclimation on chloride regulation 



In brown shrimp acclimated to and tested at 32°C, chloride in- 

 flux occurred for a maximum of two hours in 25 and 36°/ooS media 

 (Fig. 16). In 5°/ooS the salt loss continued for about four hours. 

 At lower temperatures of 25°C (Fig. 17) or 18°C (Fig. 18), the dura- 

 tion of salt influx in 25°/ooS was also the same as in 32°C. But in 



73 



