due to the temperature raise. Cases of paralysis or cramps were not 

 known. The pattern of activity level was much the same as in the 

 control--a short period of increased activity at 25°C, longer hyper- 

 activity at 32°C, and relative inactivity at 18°C. 



Effect of reduced calcium 



Reduced calcium (Ca) levels had the greatest impact on the sur- 

 vival rates of shrimp of all the ions tested. The mortality rate 

 increased roughly in proportion to the reduction of calcium ion. In 

 addition, high temperature increased the death rate (Table 26) . 



At 25°C the salinity media with 5 and 10% Ca concentration levels 

 proved to be "lethal." The term "lethal" implied that none of the 

 shrimp survived in these concentrations (Table 26) . The salinity 

 media with 15, 25, and 35-o Ca were "critical" for the survival of 

 some of the test shrimp. No deaths occurred in salinities containing 

 calcium levels above 35-0. The lethal calcium concentration range in- 

 creased to 5, 10, and 15% Ca at 32°C. The critical range included 

 25 and 35% Ca levels. In contrast to this condition, in 18°C none 

 of the reduced calcium levels were lethal for the shrimp. Calcium 

 levels 5, 10, and 15% appeared to be critical for the survival of 

 some of the shrimp only. However, at 18 °C the shrimp developed 

 muscular cramps in the reduced calcium concentrations at the rate 

 of three in 10% Ca and one each in 15 and 25% Ca. Another difference 

 was that the shrimp were more active than those in normal water of 

 15°/ooS at 18°C. 



Effect of reduced magnes ium 



The shrimp appeared more active in the reduced magnesium (Mg) 

 concentrations at the three temperatures than those from the control. 

 However, in these media the animals showed signs of stress later. 



At 25°C the shrimp became hyperactive after 20 hours in salinity 

 with 0% Mg. Two of them were under stress by eight hours in 0% Mg. 



^60 



