Figure l. — Test chambers and apparatus for testing thermal effects on Euphausia pacifica. 



ter at the acclimation temperature and main- 

 tained in the low temperature incubator. All lots 

 were checked for mortality at 5, 10, and 15 min 

 after introduction to the test temperature when 

 the duration of the exposure was 15 min and also 

 at 20 and 30 min after introduction for the 30-min 

 exposure. All were again checked at 1, 24, and 48 h 

 after testing. The 48 h survival was taken as diag- 

 nostic for the TL5o's. 



Temperature effects were evaluated on the basis 

 of mortality during tests and 48 h after testing. 

 Forty-eight hours was assumed to be a reasonable 

 holding period to check for delayed mortalities — 

 yet not long enough to cause mortality due to 

 confinement and lack of food. A euphausiid was 

 considered dead if no movement of the thoracic 

 appendages, pleopods, or antennae could be de- 

 tected using 3 X magnification. I modified the term 

 median tolerance limit (TL50) to indicate the 



maximum 15- or 30-min exposure temperature 

 survived by at least 50'7f of the experimental ani- 

 mals 48 h after testing. This should be considered 

 the maximum temperature-time combination re- 

 sisted. 



Lengths of the test animals between the ex- 

 treme tips of the rostrum and telson were taken at 

 the end of each test. The mean-lengths of the 

 euphausiids tested at the various seasons ranged 

 from 12.11 to 18.37 mm (Table 1). The actual 

 range was from 9 to 27 mm. Those tested in the 

 early part of June were the largest; they exceeded 

 those tested later in June by an average of 6.26 



Table 1.— Sizes (milHmeters) of Euphausia pacifica tested. 



897 



