EFFECTS OF ACUTE AND CHRONIC THERMAL EXPOSURES 715 



Schubel and Koo (1976) found, for example, that striped bass 

 embryos 24 to 36 hr old could tolerate a 15°C temperature elevation 

 (AT) over ambient (19— 20°C) for 5 to 15 min followed by varying 

 cooling rates. However, exposure to a 20° C AT for 5 min followed 

 by a 90-min cooling period reduced hatching success by 32%, and the 

 same AT applied for 10 min followed by a longer cooling period 

 totally eliminated any hatch. Such studies indicate that certain 

 thermal exposures, comparable to those potentially experienced by 

 embryos entrained into once-through cooling systems, can reduce 

 hatching success. 



Other investigations have considered the effects of long-term 

 temperature elevations encompassing much or all the embryonic 

 period from fertilization to hatch. Edsall (1970), for example, 

 reported that a temperature of about 26.7° C (80°F) was the upper 

 limit for successful incubation of alewife eggs. Shannon (1969) 

 found no significant difference in the hatching success of striped bass 

 eggs over the temperature range 15.5 to 24.0°C. Such studies as these 

 indicate that certain elevated temperature conditions, comparable to 

 those potentially found in thermal-discharge areas, can reduce 

 hatching success. 



In the process of assessing the thermal impact of Hudson River 

 power plants, the need arose for data concerning the effects of 

 elevated temperature on fish eggs. The Hudson River is used 

 extensively for spawning by a number of anadromous fish species 

 during the winter, spring, and early summer months. Some spawning 

 does occur in the general vicinity of the major thermal discharges on 

 the river. Consequently in 1976 a 2-year laboratory study was 

 initiated to determine the effects of both long (chronic) and short 

 (acute) exposures of elevated temperature on the hatching success of 

 the eggs of three major anadromous fishes — striped bass (Morone 

 saxatilis), alewife (Alosa pseudoharengus), and Atlantic tomcod 

 (Microgadus tomcod). The results of this study and the applications 

 of the hatching success data to thermal-impact assessment are 

 presented in this paper. 



METHODS AND MATERIALS 



The effects of elevated temperature on fish eggs were investigated 

 in a laboratory located on the banks of the Hudson River near 

 Newburgh, N. Y. (river mile 65). The laboratory water supply was 

 river water clarified by flocculation, settling, and filtration. Experi- 

 mental apparatus included eight flow-through water baths for the 



