140 



FISHERY BXJLLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 20. — Morlalities of sea lamprey eggs reared at a 

 constant temperature of 75° F. (23.9° C.) 



' Terminal sample. 



stages were reached more rapidly than at lower 

 temperatures and the overlap of stages was limited 

 (tables 6 and 19; fig. 28). 



Transition from one stage into the next was 

 rather precise, as in the two preceding experiments. 

 No stage overlapped another in more than 2 

 samples (tables 6 and 19). Stage 8 was projected 

 over 9 samples covering 24 hours as contrasted 

 with 2 or 3 for each of the earlier stages. 



Substantial mortality appeared early at this 

 temperature, especially between stages and 8. 

 The percentage of dead embryos had reached 95 

 percent on the seventh day, and the terminal 

 sample did not include any live embryos. Pro- 

 duction at this temperature was nil, despite the 

 survival of some individuals as far as stage 16. 



It is conceivable that stage 17 possibly could 

 have been reached since the experiment was termi- 

 nated when the supply of stage 16 prolarvae was 

 exhausted. Were it possible to have allowed 

 development to proceed without sampling, the 

 probability of stage 17 being reached would have 

 been improved. 



Abnormalities occurred in 35 to 40 percent of 

 the prolarvae. These abnormalities were similar 

 to those already listed except that deformed 

 specimens were especially numerous. 



E>evelopment at 77.5° F. 



A constant temperature of 77.5° F. was 

 decidedly above the maximum at which sea lam- 

 prey eggs could develop successfully. Mortality 

 was so great that all embryos were dead after 13 

 hours and none developed beyond stage 6, 32 cells 

 (tables 6, 21, and 22; fig. 27)' 



Stage 1 was taken in the 1- to 4-hour samples, 

 stage 2 in the 4- and 0-hour samples, and stage 3 



in the 6- to 10-hour samples. Only 4 embryos 

 developed beyond stage 3, and only 3 (stages 5 

 and 6) were still alive in the sample taken at 13 

 hours. All were dead in samples from 14 hours 

 to the termination of the experiment at 24 hours. 

 Some stages were reached earlier at 77.5° F. than 

 at 75° F. (stages 2 and 3), but others were attained 

 later at the higher temperatures (stages 4 and 5). 

 See table 6 and ficr. 28. 



Table 21. — Living and dead embryos per sample and their 

 stage of development at 77.6° F. (25.3° C.) 



Table 22. — Mortalities of sea lamprey eggs reared at a 

 constant temperature of 77.6° F. (25.3° C.) 



I All embryos (485) dead in the 6 samples taken after 13 hours. 



Development at 80° F. 



Developmient was brief and erratic at a con- 

 stant temperature of 80° F. A few embryos 

 reached the 32-cell stage (stage 6) but most were 

 dead long before that stage was reached (tables 

 6, 23, and 24; figs. 27 and 28). 



No signs of cleavage had appeared at the end 

 of the first 3 hours but at the fifth hour practically 

 all of the eggs had begun to dimple, the initiation 

 of first cleavage and stage 2. By the ninth hour 

 all eggs had completed first cleavage and many 

 had started the second cleavage (start of stage 

 3). At the 11th hour the pattern of cleavage had 

 become rather erratic, since the second cleavage 

 furrow often began while the first was less than 

 half-completed. At times the first cleavage fur- 

 row seemed to regress. 



Mortality which was slight in the first 2 samples 

 had risen to about 35 percent in the seventh hour. 

 All embryos were dead hi the sample at 13 hours, 

 but the next sample at 15 hours contamed eggs 



