steady metabolic rates in 5°C within two hours and showed no further 

 fluctuations in the succeeding 24 hour period. IVhen the test tempera- 

 tures were reversed from 5° to 15°C the new metabolic steady-state 

 levels were reached in about 15 hours followed by prolonged fluctua- 

 tions. It is not known why the isopods took five times longer to 

 acclimate to 15°C than to 5°C. The respiratory pattern in brown 

 shrimp at 18° and 25 °C approximate these responses; but we are not 

 sure whether the sudden drop in the respiratory rates at 18°C can 

 be termed a steady-state level. 



At 18°C the state of salinity adaptation determined on the 

 basis of osmotic and chloride regulation therefore appeared to be 

 more reliable than the exclusive respiratory responses. The meta- 

 bolic rate can be taken as a reliable criterion when the responses 

 are in harmony with the osmotic or chloride ion regulation under 

 identical test conditions. Behavioral studies of shrimp at 18°C 

 suggested that adjustment to low temperature was a slower process 

 than was indicated from the respiratory levels. 



Salinity and Temperature Requirements in Relation to Size 



In our previous studies shrimp acclimated to 21°C responded more 

 adversely to temperature changes than those acclimated to 31°C (Ven- 

 kataramiah et al. 1974). Conversely in the current experiments the 

 animals acclimated to 18°C exhibited better survival and faster sa- 

 linity acclimation than those acclimated to 32°C. The shrimp accli- 

 mated to 32°C experienced heavy mortality. The rate of salinity 

 adaptation was relatively slow. The discrepancy in the temperature 

 relationship of shrimp in the two studies may be due to size vari- 

 ations of the experimental animals. Juveniles of 70 mm average 

 length were used previously. The mean length of shrimp in these 

 studies was 95 mm. In the life cycle of brown shrimp, some impor- 

 tant physiological variations are likely to occur within these two 

 sizes. 



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