288 



BULLETIN OF THE BUREAU OF FISHERIES 



The following table gives the incubation periods of eight collections of cod eggs 

 at the Woods Hole hatchery, the first seven of which were subjected to the normal 

 winter cooling of the water: 4 



Table 10 



Date received 



Number of 

 eggs received 



Number 

 good after 

 24 hours 



Date 

 hatched 



Number of 

 eggs hatched 



Incuba- 

 tion 



period, 

 days 



Average 

 tempera- 

 ture, ° C. 



Nov. 10, 1925 



426, 000 



289,000 



Nov. 22, 1925 



184, 000 



13 



8.5 



Nov. 11, 1925 



994, 000 



910, 000 



do 



794,000 



12 



8.56 



Nov. 21, 1925 



11,361,000 



10,092,000 



Dec. 4, 1925 



9, 176, 000 



14 



6.8 



Nov 23, 1925 



16,414,000 



14,235,000 



Dec. 6, 1925 



12, 387, 000 



14 



6. 67 



Nov 28, 1925 



11, 598, 000 



10,693, 000 



Dec. 11,1925 



8, 673, 000 



14 



6.0 



Dec. 9,1925 



6,114,000 



6, 684, 000 



Dec. 28,1925 



4, 947, 000 



20 



2.83 



Dec. 15, 1925 



3, 553, 000 



3, 290, 000 



Jan. 5,1926 



2,553,000 



22 



1.56 



Jan. 1, 1926 - 



3, 532, 000 



3, 225, 000 



Jan. 19,1926 



1,613,000 



19 



3.33 



These data were prepared to serve as a comparison with the records of other 

 observers made on eggs maintained at constant temperatures. The collection 

 received on January 1, 1926, after the water had been raised artificially to a constant 

 temperature of 3.33° C, is included as a check and compares very well with the 

 following records of Ryder, Hensen, Earll, Bigelow, and Welsh. 



Table 11 



Incubation period, 

 days 



Tempera- 

 ture, ° C. 



Authority 



Incubation period, 

 days 



Tempera- 

 ture, ? C. 



Authority 



10-11 



8.33 

 7.22 

 7. 50 

 6.11 

 6.11 

 5.00 

 3.33 



Bigelow and Welsh. 



Earll. 



Hensen. 



U. S. Fisheries Manual. 

 Bigelow and Welsh. 

 Hensen. 

 Ryder. 



20 



3.00 

 3. 33-3. 89 

 3.33 

 2.20 

 .50 

 .00 

 -1.20 



Hensen. 



Bigelow and Welsh. 

 U. S. Fisheries Manual. 

 Hensen. 

 Do. 



Bigelow and Welsh. 

 Hensen. 



13 



20-23 



13 



21 



14 



24 



14-15 



34 



16 



40 or more 



20 



50- 







By comparing Tables 10 and 11 it will be seen that, in determining the length 

 of an incubation period during the fall cooling of the water, the average temperature 

 may be used. Thus, on November 21 eggs hatched in 14 days at an average temper- 

 ature of 6.8° C, which compares very well with the records of Bigelow and Welsh 

 and the United States Fisheries Manual for eggs maintained at a constant tempera- 

 ture of 6.11° C. Again, on December 9, eggs hatched in 20 days at an average 

 temperature of 2.83° C. as compared to 3° C. given by Hensen for a similar period. 

 In the light of these data it was possible to determine the approximate incubation 

 period at the time of each cruise. Using the range indicated by the mean surface 

 and bottom temperatures, the following results were obtained: 



Table 12 



Trip 



Mean sur- 

 face tem- 

 perature, 

 ° C. 



Mean bot- 

 tom tem- 

 perature, 

 0 C. 



Approxi- 

 mate incu- 

 bation pe- 

 riod, days 



Date 1924-25 





6. 14 



6.13 



14-15 



Dec. 3. 





6.20 



6. 25 



14-15 



Dec. 9-11. 





5.02 



5. 46 



15 



Dec. 16-17. 





4. 30 



4.75 



16-17 



Dec. 22-23. 





2.54 



2.60 



22 



Jan. 6-8. 





.75 



.95 



30 



Feb. 6-7. 





1. 65 



1. 68 



26-28 



Feb. 24-25. 





2.00 



1.89 



24-25 



Mar. 10. 





4.59 



3. 40 



17-20 



Apr. 7-8. 

 Apr. 21. 

 May 20-22. 





5.27 



4.02 



14H-17 



13 



8.89 



4.57 



9-17 













4 Eggs obtained from tank fishes. 



