normal activity that stabilization in the regulation took place. 

 During depression often there was a failure of the regulatory pro- 

 cesses. Burying has been recognized not only as a diurnal rhythmic 

 activity but also as a means of escape from too dilute or too saline 

 waters or from too cold or warm conditions. Burying was normal when 

 induced by one of these factors but was uncoordinated when the two 

 factors were changed simultaneously. In response to salinity or 

 temperature stress, the shrimp sometimes congregated in small groups 

 of three or four (Fig. 3a), the significance of which is not well 

 understood but which appears to be part of their responses to stress. 



Effect of salinity change 



In the present studies behavior was observed in 2, 5, 10, 15 

 (control), 25, and 36°/ooS in combination with 18°, 25° (ambient), 

 and 32 °C. Additional observations on behavior that were not re- 

 ported earlier will be presented here. Behavior in the test con- 

 ditions was compared with that of the normal behavior in control 

 conditions (15°/ooS and 25°C) . Normal behavior includes burying 

 on a diurnal basis and other routine activities such as walking, 

 swimming, or digging. About half of the animals buried in 15°/ooS 

 and 25 °C conditions during the day, the number varying from time 

 to time. Some shrimp remained motionless for several hours. Others 

 walked or swam short distances. There were no mortalities among 

 the animals acclimated and tested in 15°/ooS and 25°C (Table 1). A 

 temperature increase to 32 °C caused nine out of ten shrimp to bury 

 in 15°/ooS. Change of temperature to 18°C made them less active 

 and rarely induced burying. Survival rates were also normal at 

 these temperatures. 



Salinity change from control 15°/oo influenced the behavior 

 and survival even though the test temperature (25 °C) was the same 

 as that of acclimation (25°C). Transfer to any of the other sa- 

 linities--2, 5, 10, 25, or 36°/oo--resulted in hyperactivity as an 

 immediate response. The extent and duration of the hyperactivity 



49 



