presumably because of temperature change from acclimation. The salt 

 levels were, however, partially restored from the second day onward. 

 The effective new steady-state levels at 32° and 25°C approximated 

 closely those of shrimp acclimated and tested at 25°C (Fig. 49). The 

 osmoregulatory efficiency was disturbed further at 18°C (Fig. 54). 

 Rapid initial changes in the blood osmoconcentration occurred in all 

 salinities lasting from ten hours in 2°/ooS up to one full day in 

 36°/ooS. However, the regulatory efficiency improved in the meantime 

 and the salt concentration levels were stabilized. But the steady- 

 state levels deviated considerably from those tested at 32°C. 



The osmoconcentration pattern of animals acclimated to 18°C was 

 essentially alike when tested in 18°C (Fig. 55), 25°C (Fig. 56), and 

 32°C (Fig. 57). The fluctuations in osmoconcentration at 18°C were 

 relatively lower than in the shrimp acclimated to 25°C or 32°C and 

 tested in 18°C (Figs. 51 and 54, respectively). New steady-state 

 levels were established in all salinities from the fourth day. Osmo- 

 regulation was apparently more effective in salinities from 10 to 

 25°/oo at 25°C than at 18° or 32°C. Only minor osmotic changes ap- 

 peared at 25°C in 10, 15, and 25°/ooS. In 36°/ooS the salt influx 

 was lower than at 18° or 32°C. For some reason the regulatory pro- 

 cess in 5°/ooS appeared atypical. Oxygen consumption responses also 

 corresponded with the osmotic concentration in 5°/ooS. 



The shrimp experienced more changes in osmoconcentration at 32°C 

 (Fig. 57) than at 18° or 25°C, characterized by a greater salt influx 

 in 25 and 36°/ooS. Steady-state levels were not established in 2 and 

 36°/ooS within the one-week period. Tlie regulatory efficiency of 

 shrimp acclimated to 18°C was affected less in 32°C than those accli- 

 mated to 32°C and tested in 18°C (Fig. 54). 



Chloride concentration 



The chloride ion concentration in these experiments was found to 

 constitute approximately half of the total blood salt concentration. 



120 



