lower temperatures. The preference for high salinity and low tempera- 

 ture combinations may indicate a physiological preparation of the ju- 

 veniles for offshore emigration. On this basis a possibility for the 

 existence of seasonal salinity-temperature rhythms was suggested. 



Magnesium, calcium, and potassium ions comprised a minor portion 

 of the blood ions compared with chlorides. The concentration of these 

 ions increased with external salinity. Temperature change influenced 

 the regulation of each ion differently. Potassium exhibited a more 

 consistent temperature-related pattern than others. The behavior and 

 survival of shrimp were not significantly changed by minor changes in 

 the composition of sodium, magnesium, calcium, or potassium; but 

 major changes in calcium and potassium affected the shrimp more ad- 

 versely than other ions. 



Below 35% of the normal calcium concentration the animals started 

 dying. The death rate increased with reduction in calcium levels. In 

 5 and 10% calcium all test shrimp died. Also the death rate increased 

 with temperature. A similar trend was noticed in solutions with low 

 magnesium and to a lesser extent with low potassium. 



In media with low potassium levels there was a high incidence of 

 abdominal cramps at 18 "C. At 25° and 32 °C the incidence was none or 

 rare. Tlie cramping was observed in the behavioral studies mainly in 

 2 and 5°/ooS media at 18 °C. It was inferred, therefore, that low 

 potassium levels and low temperatures were likely combinations in 

 which abdominal cramps occur. 



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