physiological reactions. Sometimes the behavior may help to improve 

 the effectiveness of the physiological regulation. One of the im- 

 portant examples of their behavior is the seasonal southward migra- 

 tion of penaeid shrimp from Georgia to Florida (Burkenroad 1949; 

 Lindner and Anderson 1956; McCoy and Brown 1967) and from Texas to 

 Mexico (Gunter 1962) during the cold season and their return in the 

 spring. These coastal movements are only extensions of seasonal 

 movements out of the bays and shallow offshore waters in the fall 

 and return in the spring which Gunter showed in a series of studies 

 in Louisiana and Texas for the major motile species of organisms in 

 the northern Gulf. Presumably, similar seasonal movements take 

 place in all bays and shallows of the temperate zone. 



In the laboratory, brown shrimp try to escape from low tempera- 

 ture (Aldrich et al. 1968) or from extreme salinity and temperature 

 conditions (Venkataramiah et al. 1974) by burying in the substratum. 

 In addition to burying behavior when faced with stress shrimp also 

 run and swim vigorously or jump out of the tanks. Along with the 

 escape responses, the shrimp would seem to resort to simultaneous 

 physiological regulation. 



Ionic and osmotic regulation are two important aspects of the 

 physiological regulation. Ionic regulation in aquatic animals occurs 

 essentially between the external medium and the blood and between the 

 blood and tissues. In the process of ion regulation brown shrimp 

 showed significant differences between the ionic composition of the 

 blood and that of the external medium (Venkataramiah et al. 1974). 

 Sodium and chloride comprised the major blood ions. In a test salin- 

 ity range of 8.5 to 34.0°/oo these ions were maintained well above 

 the concentration levels of the external media in the low-salinity 

 range (8.5 and 17.0°/ooS). In the high salinity range (25.5 and 

 34.0°/ooS) the ions were at a lower level. On the other hand, the 

 magnesium concentration was much below the level of external sa- 

 linities throughout, while calcium was well above the level. Shrimp 



27 



