No adult shad distress or mortality took 

 place in fresh- to salt-water transfers 

 over the same temperature (experiment 7) 

 or a 16° F. temperature difference (ex- 

 perinnent 6). No mortality occurred annong 

 the controls conducted with the adult shad 

 tests . 



TOLERANCE OF JUVENILES 

 Materials and Methods 



Juvenile striped bass were obtained 

 from the Chowan River approximately 10 

 miles above Edenton, N. C, and juvenile 

 shad were obtained from the Neuse River 

 near New Bern, N. C. Striped bass ranged 

 from 3.9 to 5.7 inches fork length, and 

 shad ranged from 2.2 to 3.1 inches fork 

 length. Collections were made during the 

 months of September and October, using 

 a 70-foot bag seine. Fish were transported 

 to the laboratory by means of a 200-gallon 

 wooden tank mounted on a truck (Sykes, 

 1950). At the laboratory, each species was 

 placed in separate holding pools containing 

 Neuse River water from the seining site. 

 Subsequently, a percentage of the stock 

 fish was acclimated to salt water over a 

 24-hour period. Water temperature in the 

 stock pools ranged from 57° to 82° F., and 

 salinity in the salt-water stock pool ranged 

 from 28 to 32 ^oo . 



Equipment used in these studies con- 

 sisted of 5-gallon glass jars which were 

 used as experimental containers, and a 

 three-compartment constant temperature 

 bath which maintained desired temperatures 

 within the jars with plus or minus 1° F. 

 variation. Neuse River water (pH 7.6; sa- 

 linity range 1 to 4 oo but diluted with rain 

 water to less than 1 %o), Beaufort Channel 

 water (pH 7.4; salinity range 28 to 32 "bo), 

 and sea salt were used to prepare experi- 

 mental waters. Dissolved oxygen was main- 

 tained between 6.0 and 7.5 p. p.m. by ball- 

 type air mist releasers connected to an 

 air compressor system. 



Abrupt transfers of juvenile striped 

 bass and shad were made between salt and 

 fresh water at specific temperatures and 

 salinities over the range 45° to 70° F. and 

 to 33 ''oo, or within fresh water over 

 this same range of temperatures. Test 

 jars were filled with experimental waters, 

 and fish from the stock pools were placed 

 in those jars which served as initial en- 

 vironments. If initial environments were 



salt water, fish were taken from the salt- 

 water stock pool, and if initial environ- 

 nnents were fresh water, fish were taken 

 from the fresh-water stock pooi. 



Ten shad in a jar or ten striped bass 

 divided between two jars because of their 

 larger size constituted each test lot. Jars 

 were placed within constant temperature 

 baths at temperatures designated for the 

 tests. Fish were acclimated to the initial 

 environment for a minimum of 48 hours 

 and then transferred to the receiving en- 

 vironment. Transfer of fish from jar to 

 jar was accomplished by pouring fish and 

 water into a mounted funnel having a cloth 

 net insert, and then releasing them from 

 the net into the new container. Mortality 

 was determined 24 and 48 hours after 

 transfer to receiving environment. Cessa- 

 tion of respiratory movement was taken 

 as the criterion of death. 



Experiments were also conducted to 

 determine the ability of juvenile fish to 

 acclimate to gradual changes in tempera- 

 ture or salinity over ranges not tolerated 

 with abrupt transfer. Gradual changes in 

 temperature and salinity could not be ef- 

 fected simultaneously with experimental 

 apparatus used in this study. The rate of 

 temperature decrease in the test con- 

 tainers was controlled by the depth the 

 jars were immersed in the temperature 

 baths. Air releasers used for oxygenation 

 created enough circulation to provide uni- 

 form temperatures within the jars. Rate 

 of salinity increase was controlled by 

 adjustment of flow from a salt-water line. 

 Two striped bass tests were conducted by 

 jar-to-jar transfers in a series of "step 

 changes" in salinity with gradual decrease 

 in temperature. Controls of 10 fish each 

 were used in the juvenile studies. Con- 

 trols involved handling the fish in the same 

 manner as those of the accompanying test, 

 with no change in temperature or salinity. 



Striped Bass Experiments 



Juvenile striped bass in general were 

 tolerant to abrupt transfers between salt 

 and fresh water and to transfers within 

 fresh water at the different temperatures 

 tested. No appreciable mortality occurred 

 in transfers from fresh to salt water over 

 a temperature range of 70° to 55° F., and 

 no deaths occurred in tests conducted within 

 fresh water at decreases in temperature 

 over the same range (table 3). High 



