mm. Those tested in August, March, and April had 

 an average spread of only 1.01 mm. 



Results 



Controls in the different tests suffered no mor- 

 tality during the exposure period except the 

 June-July tests, where the 15-min group lost 7% of 

 controls by the end of 48 h and the 30-min group 

 lost 10% by the end of 48 h. The data were cor- 

 rected to reflect the loss of the controls in the 

 June-July tests, using the method of Tattersfield 

 and Morris ( 1924) as reported by Sprague ( 1969). 



Acclimation temperature influenced resistance. 

 The TL50 of euphausiids given a 15-min exposure 

 to elevated temperature was 25°C for those accli- 

 mated to 11°C; it was 23°C for those acclimated to 

 9°C. Exposure to 26°C resulted in survivals of 32% 

 and exposure to 27°C resulted in almost im- 

 mediate death ( <15 min). In the 15 min 9°C accli- 

 mation test (March-April 1974), the TL50 was at 

 23°C and 47% were still surviving 48 h after expo- 

 sure at 24°C. However, 15 min after exposure to 

 25°C, only 13% remained alive and all were dead 

 in <15 min at 26°C. Figure 2 depicts the survival 



after a 15- and 30-min exposure to elevated tem- 

 peratures and after a 48-h holding period. 



Increasing the duration of exposure to test 

 temperatures from 15 to 30 min when the ambient 

 temperature was 11°C decreased the TL50 by 1° to 

 24°C. Of those tested at 25°C, only 44% survived 48 

 h after testing. At 26°C, only 2.5% survived the 

 30-min test period. None survived the test period 

 at 27°C. 



The logistic model was fitted to the data from 

 the three different thermal shock tests. The prob- 

 ability of survival was taken to be the form 

 P [survival at temperatures] = l/d+e"*^''^ where 

 e = 2.718. This is the so-called logistic model and a 

 and b are parameters which are estimated using 

 the data. In the 15-min exposure of June-July 

 1971, a = 0.6544 and h = -16.4138; in the 

 March-April 1974 exposure, a = 0.9568 and b = 

 -22.2860; whereas in the 30-min exposure July- 

 August 1971, d = 0.5173 and b = -12.2572. The 

 estimates of TL50 and an approximate 95% 

 confidence interval for it follow for the three tests: 

 1) 25.08°C, 24.51°-25.65°C; 2) 23.29°C, 22.76°- 

 23.82°C; and 3) 23.69°C, 22.95°-24.44°C. 



There was no obvious difference in the effect of a 



I5MIN 



o</A- 



100 p 

 90 - 

 80 



70 



% 60 



> 



CO 



I I I I i_l 1 l_i I . I  l_i I 1 I V I . I 



10 12 14 16 18 20 22 24 26 28 30 

 TEST TEMP (°C) 



30 MIN 



/^ 



48 H ""^ / 



V 



JUNE - JULY 



50 



40 - 



30 - 



20 - 



10 - 



V/^ 

 8 



\ / 



50% ^ 



30 MIN EX 



-1— J — l-j 1—1 1 ] I I I . I 



I . J 



10 12 14 16 18 20 22 24 26 28 30 

 TEST TEMP t°C) 



100 

 90 

 80 



I 60 



a: 50 



I5MIN 



30 - 

 20 - 

 10 - 

 Ly/ 



48 H 



MARCH -APRIL 



50% — 



15 MIN EX 



I . I 



I  I  I  I  I  I 



I I ] 



8 10 12 14 16 18 20 22 24 26 28 30 

 TEST TEMP (°C) 



Figure 2. — Survival (including mean and range) ofEuphausia 

 pacifica after 15- or 30-min exposures to elevated temperatures 

 and subsequent holding at 9° or \\°C ambient temperatures for 

 48 h. 



898 



