increased with the degree of deviation of the test concentrations 

 from control. Hyperactive shrimp stayed in almost constant motion, 

 either walking on the bottom or swimming around. The hyperactivity 

 ceased within one hour in 5, 10, and 25°/oo, within two hours in 

 36°/oo and in three hours in 2°/ooS. In salinities 5°/oo and above 

 the animals resumed normal activity for the remainder of the test 

 period. In 25 and 36°/ooS more shrimp (five or six) buried compared 

 with one or two in 5 or 10°/ooS. Mortality rates are reported in 

 Table 1. Most of the deaths which occurred in these concentrations 

 were due to molting. Often the freshly molted shrimp were attacked 

 and killed by other normal animals. 



In 2°/ooS the shrimp had disoriented movements (Fig. 3b) and 

 convulsions. Some evidenced symptoms of stress within one or two 

 hours, lying on their sides twitching their legs. Half of the 

 animals died within 12 hours but the others adjusted and showed 

 almost normal but subdued activity. 



Effect of temperature background 



Shrimp acclimated and then tested at 18° and 32 °C did not show 

 much initial hyperactivity in the test salinities except in 2°/oo. 

 Shrimp from 18°C were hyperactive in 2°/ooS for 1/2 hour while those 

 from 32 °C remained hyperactive for two hours. In 2 and 5°/ooS the 

 death rate was generally high, not considering those which occurred 

 from molting (Ref. Table 1). The surviving shrimp at 32°C were 

 inactive; at 18°C they were depressed. Some shrimp buried but the 

 rate was higher at 32°C. A maximum number of animals (six to ten) 

 buried in 15°/ooS at 32°C. At 18°C all but one or two remained buried 

 in 36°/ooS throughout. In other salinities fewer animals buried. 



In 18°C shrimp developed abdominal (tail) cramps, a condition 

 which appeared almost exclusively under low salinity and low tem- 

 perature 18°C conditions. Within 1/2 to 2-1/2 hours all the shrimp 



52 



