My experiments indicate that an increase of 

 6°C in the area of an outfall could cause TD50 in 

 about 168 h (7 days) among important segments 

 of the reproducing population. To minimize dam- 

 age to Daphnia populations in the Columbia 

 River, the temperature should not be raised more 

 than 6°C above ambient or higher than 26° or 

 27 °C for any prolonged period. 



A short exposure (15 min) to increased temper- 

 atures as might occur in a condenser cooling sys- 

 tem did not cause a significant reduction in time 

 to TD50 or in reproduction unless the temperature 

 exceeded 30°C. There is a period from mid-July 

 through September when the lower Columbia 

 River temperatures may exceed 20°C. In these 

 instances, the temperature increase in condenser 

 cooling systems should be less than 10°C if the 

 Daphnia are to survive. It must be kept in mind 

 that temperature is only one of several factors 

 including pressure, abrasion, and toxic chemicals 

 that could be acting synergistically to damage 

 zooplankton in a condenser cooling system 

 (Marcy 1973; Becker and Thatcher'*). 



To protect D. pulex populations, water temper- 

 atures in condenser cooling systems should not 

 exceed 30°C and passage through the system 

 should take less than 15 min. 



ACKNOWLEDGMENTS 



Rufus W. Kiser, CentraUa College, Centralia, 

 Wash., verified the identification o{ the Daphnia. 

 Donald D. Worlund and Frank J. Ossiander pro- 

 vided advice on statistical treatment. Linda Street 

 McCune assisted in all aspects of culturing and 

 testing Daphnia 



"Becker, C. D., and T. O. Thatcher. 1973. Toxicity of power 

 plant chemicals to aquatic life. Battelle Mem. Inst., Pac. North- 

 west Lab., Richland, Wash., rep. for U.S. At. Energy Comm., 

 WASH-1249, UC-11, misc. pagination. 



FISHERY BULLETIN: VOL. 74, NO. 2 



LITERATURE CITED 



American public health association. 



1971. Standard methods for the examination of water and 

 wastewater. 13th ed. Am. Publ. Health Assoc, Wash., 

 D.C., 874 p. 

 COUTANT, C. C. 



1970. Entrainment in cooHng waters: steps toward predic- 

 tability. Proc. 50th Annu. Conf. West. Assoc. State Game 

 Fish Comm., p. 90-105. 



DOUDOROFF, P., B. G. ANDERSON, G. E. BURDICK, P. S. 

 GALTSOFF, W. B. HART, R. PATRICK, E. R. STRONG, E. W. 



Surber, and W. M. Van Horn. 



1951. Bio-assay methods for the evaluation of acute toxicity 

 of industrial wastes to fish. Sewage Ind. Wastes 

 23:1380-1397. 

 Ivleva, I. V. 



1969. Mass cultivation of invertebrates. Biology and 

 methods. Izd. "Nauka", Moscow. (Translated by Israel 

 Prog. Sci. Transl., 1973, 148 p.; available U.S. Dep. Com- 

 mer, Natl. Tech. Inf. Serv., Springfield, VA, as TT 65- 

 50098.) 



Marcy, B. C, Jr. 



1973. Vulnerability and survival of young Connecticut 

 River fish entrained at a nuclear power plant. J. Fish. 

 Res. Board Can. 30:1195-1203. 

 NORTH, W. J., AND J. R. ADAMS. 



1969. The status of thermal discharges on the Pacific 

 Coast. Chesapeake Sci. 10:139-144. 

 PRATT, D. M. 



1943. Analysis of population development in Daphnia at 

 different temperatures. Biol. Bull. (Woods Hole) 85:116- 

 140. 

 SNYDER, G. R., AND R. J. MCCONNELL. 



1971. Subsurface water temperatures of the Columbia 

 River at Prescott, Oregon (Hiver mile 72), 1968-69. U.S. 

 Dep. Commer., NCAA, Natl. Mar. Fish. Serv., Data Rep. 

 53, 9 p. on 1 microfiche. 



SPRAGUE, J. B. 



1973. The ABC's ofPollutantBioassay using fish. Am. Soc. 

 Test. Mater., Spec. Tech. Publ. 528:6-30. 



Taub, F. B., and a. M. Dollar 



1968. The nutritional inadequacy of Chlorella and 

 Chlamydomonas as food for Daphnia pulex. Limnol. 

 Oceanogr. 13:607-617. 



Tauson, a. 



1931. Die Wirking der ausseren Bedingungen auf die Ver- 

 anderung des Geschlechts und auf die Entwicklung von 

 Daphnia pulex De Geer. Wilhelm Roux Arch. Ent- 

 wicklungsmech. Org. 123:80-131. 



408 



