years, and most males mature at 2 years 

 (Raney, 1952). Approximately 65,000 eggs 

 are produced by a 4-year-old female, and 

 4,500,000 eggs are produced by a 13- or 

 14-year-old fish (Raney, 1958). Time and 

 pattern of movements of young and adult 

 vary with different populations. 



American shad are the largest mem- 

 bers of the herring family (Clupeidae) in 

 the United States. Their range extends from 

 the St. Lawrence River, Canada, to the 

 St. Johns River, Fla. Shad were success- 

 fully introduced on the Pacific coast in 187 1 , 

 and their range now extends from Alaska 

 to southern California. They are anadrom- 

 ous, and spawning migrations on the Atlantic 

 coast begin as early as November in the 

 south and are progressively later north- 

 ward. Spawning migrations on the Pacific 

 coast occur during spring and summer. 

 The number of eggs produced per female 

 each season averages about 250,000 (Talbot 

 and Sykes, 1958). The young spend the first 

 summer of life in the rivers (5 to 6 months) 

 and then nnigrate to sea. In 3 to 6 years 

 they reach sexual maturity and return to 

 their native rivers to spawn. On the Atlantic 

 coast, shad native to northern rivers return 

 to spawn in successive years. Fish native 

 to rivers south of Chesapeake Bay, and 

 particularly south of North Carolina, die 

 after spawning (Talbot and Sykes, 1958). 



TOLERANCE OF ADULTS 

 Materials and Methods 



Adult fish were obtained during Feb- 

 ruary, March, and April from commercial 

 pound-net fishermen. Striped bass were 

 obtained in Albemarle Sound nearMackeys, 

 N. C. (salinity less than I %o , tenriperature 

 51° to 69° F.j, and shad were obtained at 

 the mouth of the Neuse River near Cedar 

 Island, N. C. (salinity 1 to 17 oo, tem- 

 perature 45° to 58° F.). Striped bass ranged 

 from 12 to 24 inches fork length, and shad 

 ranged from 15 to 19 inches fork length. 

 The fish were transported to the laboratory 

 by means of a 200-gallon wooden tank 

 mounted on a truck (Sykes, 1950). At the 

 laboratory, fish were dipped for 20 seconds 

 into a malachite green solution (1:15,000) 

 to prevent fungus infection and placed in 

 holding ponds. 



Three rectangular concrete pools and 

 two ponds were used in these studies. The 

 pools were 6 feet by 16 feet by Zj feet deep 



and were supplied with salt and fresh 

 water. The pH of the pools during the 

 tests was 7.4 to 7.6, and dissolved oxy- 

 gen remained above 6.0 p. p.m. The ponds 

 were 30 feet by 40 feet, and their 

 depth varied from 1 to 4 feet. Each pond 

 was divided into two sections by a hardware 

 cloth fence, one section for holding stock 

 fish and the other for experimental use. 

 One pond was continuously supplied with 

 sea water (salinity range 23 to 36 nr,)and the 

 other with fresh water. The pH of the ponds 

 ranged from 7.3 to 7.8, dissolved oxygen 

 ranged from 9.5 to 10.5 p. p.m., and tem- 

 perature ranged from 44° to 86° F. 



Abrupt transfers of adult striped bass 

 and shad were made from salt to fresh 

 water and from fresh to salt water at specific 

 temperatures and salinities over the range 

 45° to 80° F. and to 35 °oo . Temperature 

 could be regulated only in the pools as it 

 was not feasible to consider temperature 

 control for the large ponds. Desired tem- 

 peratures were obtained by heating with 

 Calrod units or cooling with ice. When ice 

 was used in salt water, sea salt was added 

 as necessary, to maintain proper salinity. 



Test transfers were made from the 

 small rectangular pools (initial environ- 

 ment) to the large ponds (receiving en- 

 vironment). The ponds were used for the 

 receiving environment as mortalities oc- 

 curred among the larger fish after 4 or 5 

 days' confinement in the rectangular pools, 

 apparently because of crowding. Experi- 

 mental fish were marked so that each 

 specimen could be identified. 



Tests were carried out by placing 10 

 fish (if available) of random size in each 

 of the rectangular pools. One pool served 

 as a control. In tests where initial en- 

 vironment was salt water, fish were taken 

 from the salt-water holding pond. In tests 

 in which initial environment was fresh 

 water, fish were taken from the fresh- 

 water holding pond. All pools contained 

 water at the same salinity and temperature 

 as the holding ponds from w^hich the fish 

 were taken. For a 24-hour period the fish 

 were acclimated to initial environment by 

 gradually changing the temperature and sa- 

 linity of the water in the pools over a 6- 

 to 8-hour period and maintaining these con- 

 ditions for an additional 16 to 18 hours. 

 The fish were then transferred into either 

 the fresh- or salt-water pond (receiving 

 environment) at the prevailing water 



