PHYSIOLOGY AND BEHAVIOR PROGRAM 



David V. Aldrich, Program Leader 



Since midyear, this program has been specifically directed toward 

 laboratory experiments dealing with the environmental requirements of com- 

 mercial shrimps, primarily in postlarval and juvenile stages of development. 

 One goal - to determine limiting and optimal levels of salinity and tempera- 

 ture - is being approached in three ways: (1) observing survival of shrimp ex- 

 posed to known salinity and temperature combinations, (2) observing the se- 

 lection of a temperature or salinity range by shrimp placed within a continuous 

 linear gradient, and (3) comparing the growth rates of shrimp held at known 

 salinity and temperature conditions. 



Much of our progress has been made possible by adapting available 

 equipment and developing new devices. Examples of this type of activity are 

 the successful modification of laboratory incubators for survival studies, com- 

 pletion of vertical water columns with salinity and temperature gradients for 

 behavior experiments, development of a method for preventing postlarval 

 shrimp from junnping above the water's surface in aquaria (reducing "false 

 mortality" during growth and survival studies), and finding a practical lab- 

 oratory diet for small shrimp. 



Laboratory results obtained using brown shrimp, Penaeus aztecus, 

 indicate that postlarval as well as juvenile stages can tolerate a wide range of 

 salinity levels (5%o-35%o). It is particularly noteworthy that this conclusion is 

 based not only on the results of short-run survival experiments but also on the 

 more sensitive indices of environmental suitability provided by behavior and 

 grovi^h studies. The survival work further showed that the range of tolerance 

 to salinity narrowed considerably at the lowest temperature level tested 

 (7» C.). 



Preliminary results of comparative survival experiments suggest 

 that juvenile shrimp tolerate a wider range of temperatures than do postlarvae. 

 Such physiological changes during development within a species may have an 

 important bearing on the patterns of distribution and movement characteristic 

 of young shrimp. It may be that the relatively stable temperature of offshore 

 spawning grounds is more conducive to the survival of larvae and early post- 

 larvae, whereas the larger and hardier forms can tolerate the less static con- 

 ditions encountered in the more fertile nursery areas of the bays. 



We hope that another sensitive physiological index - oxygen 

 consumption - can also be used to measure influences of environmental factors 

 on shrimp. To this end, potential anesthetics are being tested in an effort to 

 stabilize physical activity and thus permit accurate assessment of basal met- 

 abolic activity through measurennent of oxygen consumption. 



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