(Fig. 87) . The criterion for efficient regulation is the ability of 

 animals to maintain relatively steady osmotic or ionic levels in re- 

 lation to large changes in the test salinities. On this basis, the 

 osmoregulation at 25°C appeared to be more efficient than in 32° or 

 18°C. In 2, 5, and 10°/ooS the animals tested at 25°C and 32°C reg- 

 ulated the salt levels more effectively than in 18°C. In 25 and 

 36°/ooS the osmoregulation was relatively more efficient at 25° than 

 in 32°C. In 36°/ooS brown shrimp were less efficient in controlling 

 the influx of salts at 18° and 32°C. At 18°C the animals tended to 

 lose the salts initially to the dilute media. Subsequently, the 

 losses were partially recovered with the result that the final steady- 

 state levels were similar to the levels in 25° and 32°C. 



Acclimation to 32°C seemed to impair the osmoregulatory ability, 

 particularly in 2 and 36°/ooS (Fig- 86) throughout the test tempera- 

 ture range. The animals tested at 25 °C recovered from the salinity 

 stress in 2°/ooS faster than in 18° or 32°C. At 18°C the shrimp 

 failed to control the salt influx for 24 hours in 36°/ooS. In this 

 salinity the shrimp tested at 25° and 32°C appeared to be better 

 regulators than in 18°C. But the regulatory fluctuations were larger 

 in 32°C than in 25°C. Acclimation to 32°C, however, conferred cer- 

 tain advantages to the shrimp in 5 and 10°/ooS and 32 °C combinations, 

 particularly in 10°/ooS. The salt concentration levels at 18°C were 

 relatively low in most of the dilute media. 



The shrimp exhibited better regulatory efficiency when accli- 

 mated and tested at 18°C (Fig, 87). This was shown from the fact 

 that the shrimp did not experience the initial rapid salt loss in 

 2, 5, and 10°/ooS as the shrimp did when acclimated to 25° or 32 °C 

 and tested in 18°C. The osmoconcentration levels in these salini- 

 ties were maintained on par with those in 25°C; but the shrimp ex- 

 perienced severe osmotic problems in 2 and 36°/ooS at 32 °C. In 

 2°/ooS they failed in controlling the salt efflux effectively. In 



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