same temperature; however, all but one 

 survived a 4.5-hour increase. 



The interval between initial distress 

 (loss of equilibrium) and death of juvenile 

 shad (also striped bass) was usually less 

 than 1 hour when resulting from abrupt 

 transfers over extreme diffarences in tem- 

 perature and salinity. When these differ- 

 ences were slight, however, young shad 



TABLE 5, --Abrupt transfers of juvenile American shad from fresh 

 water to fresh or salt water at different temperatures 

 [Ten fish in each test] 



TABLE 7. --Acclimation of Juvenile American ahad to gradual decrease in 

 temperature and increase in salinity 



^ Two survivors in distress. 

 ^ Four survivors in distress. 



TABLE 6.--Abrijpt transfers of juvenile American shod from fresh 

 or salt water to fresh water at different temperatures 

 [Ten fish in each test] 



Only six shad were successfully accliinated for this test. 



' Two survivors in distress. 



often remained inverted at the bottom of 

 the experimental containers, except for 

 erratic swimming spurts, for as long as 

 10 hours before death. 



DISCUSSION 



Differences in the physiological de- 

 velopment of the fish might explain why 

 mortality of adult shad was greater in 

 salt to fresh water transfers at the same 

 temperature than from similar transfers 

 at a 10° F. difference in temperature. The 

 former tests were conducted 2 to 3 weeks 

 earlier than the latter, and, therefore, the 

 fish in the earlier transfers may not have 

 undergone as complete a physiological ad- 

 justment in preparation for migration into 

 fresh water. Black (1957) stated that ana- 

 dromous fishes were able to migrate be- 

 cause of normal activity that resulted in the 

 physiological changes required for survival 

 in the new environment. Black cited work 

 by Sawyer on sea lannprey (Petromyzon 

 marinus) which showed that fish migrating 

 from the sea to fresh water assumed very 

 quickly the functions of typical fresh water 

 fishes. The cause of the conflicting results 

 which occurred in transfers of adult shad 

 from salt to fresh water may also have 

 been due to individual variation. Sumner 

 (1906) stated that the capacity of different 

 individuals to endure transfers between salt 

 and fresh water varied greatly, depending 

 upon the condition of the fish. 



Juvenile shad transferred from fresh 

 to salt water could not survive compara- 

 tively small differences in temperature 



