Osmotic and Ionic Regulation in Relation to the Isosmotic Line 



In Figures 80 to 84 the isosmotic lines represent the concentra- 

 tion levels of the respective ions in the external test salinities 

 ranging from 2 to 36°/ooS. The figures were drawn with the mean os- 

 motic and ionic concentration values in the different experimental 

 conditions. The mean concentration values were computed from the 

 new steady-state levels. In some conditions new steady -state levels 

 were not established. Mean stabilization values were used in such 

 cases. 



Osmoregulation 



The osmoconcentration values for brown shrimp acclimated to 18°, 

 25°, and 32°C are shown in Fig. 80. Regardless of test temperature, 

 blood salt concentration increased with increasing salinity. How- 

 ever, the osmoconcentration appeared to be more efficient in the 

 range of 5 to 25°/ooS than in other salinities. Within this sa- 

 linity range the blood osmoconcentration was subjected to relatively 

 less change in relation to the test salinities. Outside this range 

 there was either a greater salt efflux or influx. The blood salt 

 concentration was isosmotic at about 25°/ooS level or slightly below. 



Shrimp acclimated to 25°C showed less osmoregulatory variation 

 in response to temperature changes. In contrast the shrimp accli- 

 mated to 32 °C became more temperature sensitive. The extent of the 

 sensitivity to test temperatures was determined on the basis of 

 separation of the temperature related osmotic curves from each 

 other. Moreover the osmoregulatory efficiency seemed to be im- 

 paired more in dilute salinities than in other shrimp acclimated 

 and tested at 18° or 32°C. These animals experienced a sudden drop 

 in the salt concentration levels in salinities below 10°/ooS. At 

 25°C a similar drop occurred in 2°/ooS only. 



152 



