respiratory rates indicate reduced motor activity in the respective 

 combinations. These combinations associated with low respiratory 

 rates approximate the seasonal habitat conditions of brown shrimp. 



Another important observation was made in the present behavioral 

 studies. The survival rates were generally high in 25 and 36°/ooS 

 regardless of temperature as opposed to 18°C and 2 and 5°/ooS combi- 

 nations. However, when the transfer was made directly from 15°/oo 

 to 36°/ooS the salinity adaptation was either slow or did not occur 

 at both 18° and 32°C. In nature such an abrupt change from 15 to 

 36°/ooS is unnatural. In the course of offshore emigration the shrimp 

 are exposed to high salinities in stepwise increments. In laboratory 

 experiments the shrimp did not exhibit great variations in 25°/oo 

 from 15°/ooS either in osmotic or in chloride regulation regardless 

 of test temperatures. The shrimp responded as if they were more 

 favorably inclined toward a higher salinity than the 70 mm long 

 shrimp. The optimal salinity range of the smaller juveniles seemed 

 to exist in a concentration range of 8.5 and 17.0°/ooS. Significant 

 differences were also observed in other physiological responses be- 

 tween low and high salinities (Venkataramiah et al . 1974). 



Osmoregulation and Energy Relations 



Brown shrimp acclimated and tested at 25°C exhibited hyperosmotic 

 regulation in 2, 5, and 10°/ooS and hyposmotic regulation in 25 and 

 36°/ooS with respect to the test salinities. The magnitude of the 

 osmotic or chloride changes was roughly in proportion to the devia- 

 tion of test salinities from 15°/ooS. Corresponding increases in the 

 oxygen uptake were observed in the respective test conditions. The re- 

 sponse pattern suggested a positive interaction between the respiratory 

 rates on the one hand and the osmotic and chloride regulation on the 

 other. In Pachygrapsus crassipes . Gross (1957) observed a similar in- 

 crease in the oxygen consumption in salinities other than the control. 



287 



