Osmoconcentration 



Shrimp acclimated to 15°/ooS and 25°C and tested at 25°C (Fig. 49) 

 exhibited hyposmotic blood concentration in 2, 5, and 10°/ooS and hyper- 

 osmotic concentration in 25 and 36°/ooS in relation to that of shrimp in 

 the control salinity. The magnitude of changes in osmoconcentration in- 

 creased with the deviation of the test media from 15°/ooS. Temperature 

 change from 25°C also influenced the osmoconcentration. Greater osmotic 

 changes occurred in 5, 10, and 25°/ooS when temperatures were changed 

 from 25° to 32°C (Fig. 50) or 18°C (Fig. 51). The general pattern of 

 osmotic concentrations was otherwise similar at the three test tempera- 

 tures. 



In 2, 5, and lO^/ooS there was a sudden loss of blood salts during 

 the initial six hours after transfer to 18°C (Fig. 51). In 36°/ooS the 

 salt influx continued for a whole day. However, in the process of sta- 

 bilization the initial osmotic changes were partially rectified between 

 the first and fourth days. Tlie new steady-state levels at 18°C were 

 not significantly different from those of other test temperatures. 



Shrimp acclimated to 32''C and tested at 32°C (Fig. 52), 25°C (Fig. 

 53) , and 18°C (Fig. 54) demonstrated the same pattern of hyposmotic and 

 hyperosmotic concentration levels as those acclimated to 25°C or 18°C. 

 Nevertheless, the regulatory efficiency was hindered to some extent at 

 32°C. Due to this impairment, osmotic changes of greater magnitude 

 occurred among shrimp in 2, 5, 10, and 36°/ooS than in those acclimated 

 to 25°C and tested in 32°C (Figs. 50 and 52). The osmotic changes at 

 32°C were still in progress in 2, 5, and 36°/ooS by the end of the study, 

 implying a slower rate of acclimation to those conditions. 



Shrimp acclimated to 32°C appeared to be more efficient osmo- 

 regulators in 25°C (Fig. 53) than in their acclimation temperature. 

 Tliis was particularly true in the low salinity range. At 25°C, the 

 initial salt loss was more rapid in the dilute media than in 32°C, 



113 



