FISHEKY BULLETIN VOL. 77. NO, :i 



5 10 15 20 



Incubation Time (days) 



Figure 5. — Hatching success of Acartia californiensis eggs at: 

 (A) 21° C, (B) 17° C, (C) 13° C, ID) 9° C in 25%« salinity. Eggs 

 spawned at different parental acclimation temperatures of 21°. 

 17°, 13°, and 9° C. Spaw-ning temperatures are designated by I Si. 

 Hatching temperatures increased to 21° C on day II iCi and 15 

 iDi 



holding period at 9° C (Figure 5D). Only GCK* of the 

 remaining eggs hatched following the tempera- 

 ture rise, resulting in a cumulative total of 74*^^. 



E 

 o 20 



Hatching Temperature 

 (5°C) 



2r(S) 17-(S1 



^-: -;-v- -:--:-4 

 .III / 1 \ ' < \ 



-^ 



4 6 120 124 126 



Incubotion Time (days) 



Figure 6. — Hatchmg success of Acartia californiensis eggs at 5° 

 C in 25%o .salinity. Eggs spawned at 21°, 17°, 13°, and 9° C, 

 Spawning temperature is designated by (S). Hatching tempera- 

 ture increased to 21° C on day 120. 



Long-term survival of summer eggs was negli- 

 gible at low temperature ( 120 days at 5° C). Only 

 l'7r of the 17° C spawned eggs subsequently 

 hatched at 21° C. Many of the eggs remained nor- 

 mal in appearance, being greenish yellow, 

 throughout the 120-day period. However, within 

 3-4 days at 2 rC, nearly all dormant summer eggs 

 had disintegrated. Most eggs probably died long 

 before day 120, given the high mortality of 21° C 

 spawned eggs after 15 days at 9 C (Figure 5D). 



In comparison with dormant summer eggs, the 

 eggs spawned at 13° and 9° C appear to be true 

 resting eggs with an overwintering capacity. The 

 final cumulative hatch of the two types of eggs was 

 similar over the temperature range of 21 -9° C. 

 However, there were major differences in hatch- 

 ing rates between eggs spawned at 9°-13° C and 

 17°-21° C at all five hatching temperatures tested 

 (Figures 5, 6). For example, the 9°-13° C spawned 

 eggs required 11 and 20 days at 21° and 17° C, 

 respectively, to reach the final comparable hatch 

 of 87-99%. This period was 10-20 times longer 

 than that required by summer eggs. 



While none of the 9°-13° C spawned eggs exhi- 

 bited dormancy at 17° and 21° C, few hatched at 

 the lower incubation temperatures. Only 3-49( 

 hatched at 13° C in contrast to 70-90% for the 

 summer eggs. Likewise only 0-1% at 9° C and 0% 

 at 5° C hatched versus 35% and 5-109f, respec- 

 tively, for the summer type (Figures 5D, 6). 



Temperature was increased to21°C on days 11, 

 15, and 120 for the 13°, 9°, and 5° C hatching 

 treatments, respectively. Hatching resumed in all 

 cases at a rate and with success similar to those of 

 summer eggs. However, a l-1.5day delay occurred 

 in each case before hatching resumed (Hgures 5C, 



574 



