5, and 36°/ooS after three days. Conversely, steady-state osmotic 

 and chloride ion levels were attained within the first day in all 

 salinities except in 5°/ooS. 



In 18°C test conditions the metabolic rates reached stable 

 levels sooner than the osmotic and chloride levels. The tempera- 

 ture increase was shown to influence the respiratory rates more 

 than the osmotic or ionic regulation. Naturally this would result 

 in a lack of harmony between the two responses in the process of 

 adaptation. 



The mortality was very high in shrimp acclimated to 18° and 

 tested in 32°C. The shrimp used for oxygen studies died in 2°/ooS 

 within four hours. In six days there was a similar mortality in 

 25°/ooS. Survival was generally poor in 5 and 36°/ooS. However, 

 in 10 and 15°/ooS new steady-state levels appeared both in metabolic 

 and salt regulation within the first day. In the animals that sur- 

 vived in 36°/ooS steady metabolic and chloride levels appeared after 

 four days. In 25°/ooS the deaths occurred much later after reaching 

 a steady-state metabolic level on the first day. In 2 and 36°/ooS 

 the animals failed to reach steady-state levels. Sudden temperature 

 change from 25° to 18° or 32°C obviously reduced the range of sa- 

 linity adaptation from 5 to 25°/ooS. 



The shrimp acclimated to 32 °C experienced a heavy mortality in 

 2°/ooS in the three test temperatures. At 18°C the animals used for 

 the oxygen studies survived in 2°/ooS for six hours only. In the 

 other salinities death rate was moderate to high. One possible ex- 

 planation for a higher mortality rate at 32°C than in test tempera- 

 tures 18° or 25°C was the starvation effect. Starvation was shown 

 to lower the respiratory rates; but its effects on the salt regula- 

 tion on a short-term basis were not known. Newell (1973) observed 

 that starvation may reduce the scope for activity in the intertidal 



280 



