The shrimp acclimated to 32°C (Fig. 68 a, b, c,) maintained a 

 higher mean control ion concentration (22.8 mEq/L) than those acclimated 

 to 25°C (19.7 mEq/L). At 32°C (Fig 68c) the calcium ion was controlled 

 effectively on the first day with little variation. On the second and 

 third days, however, the variations increased considerably. The cal- 

 cium ion levels were hyposmotic in 2 and 5°/ooS, hyperosmotic in 25 and 

 36°/ooS, and isosmotic in 10°/ooS with respect to the ionic concentra- 

 tion of shrimp in 15°/ooS. At 25°C (Fig. 68b) the calcium ion level 

 was hyperosmotic only in 36°/ooS. Furthermore, greater ionic fluctua- 

 tions were observed in animals tested at 25° and 18°C than in the control 

 shrimp; also the hyposmotic and hyperosmotic ion concentration patterns 

 were similar in the various salinities. However, at 18°C (Fig. 68a) 

 the salinity-related calcium curves were widely separated from each 

 other as opposed to 32°C (Fig. 68c) . The animals tested at 25°C (Fig. 

 68b) represent an intermediate trend between 18° and 32°C. The wide 

 separation of the curves may indicate a possible interaction between 

 salinity and temperature on calcium content. 



In shrimp acclimated and tested at 18°C (Fig. 69a) the initial 

 calcium concentration levels were maintained below the control 15°/ooS 

 level. The ion concentration increased above the 15°/ooS level after 

 ten hours in 36°/ooS and after two days in 25°/ooS. As a result, in 

 both salinities the calcium ion concentration became hyperosmotic. 

 In other media it was hyposmotic throughout and levels were lower than 

 in 25° and 32°C (Figs. 69b and 69c, respectively) and in the corre- 

 sponding salinities. The response pattern at 32°C was similar to that 

 in 18°C, except that the final steady-state levels at 32°C were rela- 

 tively higher. At 25°C the ion levels in salinities 25°/oo and 

 below were hyposmotic while the calcium increments in 2, 5, and 

 10°/ooS were disproportionate. The variations in the calcium con- 

 centration levels between the salinities were lowest at 32°C, ex- 

 cluding 2°/ooS. The variations increased progressively as the test 

 temperatures were lowered to 25° and 18°C. 



136 



