120 



Part III. — Twenty -seventh, Annual Report 



Summary. 



Table showing the Periods of Incubation for each lot of Spawn. 



The average temperature over the period is obtained from the maximum and 

 minimum observed temperatures of each day. Every temperature 

 observation was, therefore, not made use of. The data given in the 

 tables above are the material used. Degrees centigrade. 









Temperature of the 









Date 

 of 

 Fertili- 







Water. 







Length of 





Cooled or 

 Uncooled. 











Period of 

 Incubation. 



Lot. 





Kange. 





Period 

 of Incubation. 





zation. 





Table, 

 page 







Aver- 

 age. 









M. 



m. 









1908. 

















I. 



Feb. 18 



Partly cooled. 



106 



8-3 



—1-8 



4 



Feb. 18 to Mar. 25 



29 to 35 days. 



II. 



55 55 



5 5 5 5 



106 



8-3 



—1-6 



4-2 



55 55 55 



28 to 34 days. 



III. 



5, 19 



5 5 5 5 



106 



87 



— -4 



4-4 



„ 19 „ 



Ic. 



„ 18 



Cooled. 



108 



5-6 



—1-6 



1-4 



None hatched. 



He. 



5 5 5 5 





108 



6 



—1-6 



1-4 



5 5 5 5 





IIIc. 



„ 19 



55 



108 



4 



—1-6 



2-1 







IV. 



5, 29 



Uncooled. 



110 



6-4 



2-8 



4-8 



Feb. 29 to April 5 



23 to 36 days. 



IVc. 



5 5 5 5 



Cooled. 



113 



4-2 



— -4 



1-8 



20 



46 to 51 days. 



IVc. 1 



5 5 5 5 



55 



Partly cooled. 



113 



5-8 



1 



2-1 



5 5 5 5 25 



46 to 56 days. 



IVc. 2 



55 55 



Mar. 5 



113 



5-2 



1 



3-2 



10 



28 to 41 days. 



V. 



Uncooled. 



115 



8-2 



4-2 



5-5 



Mar. 5 to April 12 



20 to 34 days. 



Vc. 



5 5 5 5 



Cooled. 



118 



4-6 



1 



2-6 



27 



37 to 52 days. 



Vc. 1 



5 5 5 5 



j> 



118 



4-6 



•8 



2-3 



28 



41 to 53 days. 



Vc. 2 



5 5 5 5 



5 5 



Partly cooled. 



118 



7 9 



•6 



3-7 



17 



Sep. 8 to Sep. 19 et. seq. 



35 to 42 days. 



VI. 



Sept. 8 





13 



—6-6 





11 to * days. 



* The upper limit of the incubation-period was not noted. 



The experiments show that the period of incubation of the eggs of the 

 North Sea herring may be extended to 50 days, if the eggs are kept in 

 water of a sufficiently low temperature. From the extensive range of 

 temperature to which the various batches of eggs -were subjected, it is seen 

 that the ova are able to withstand changes in temperature very well. A 

 noticeable case is the last (VI.) in the table just given, where the barrel 

 containing the spawn was suddenly plunged from the warm temperature of 

 a September day* into a cold store at — 6*6° C. (p. 119). On the following 

 day the ova were put into water of 12° C. Nevertheless a large quantity of 

 the fry hatched out. 



Very low temperatures, e.g., below zero CO, were not often reached, but in 

 several instances eggs which had been for a short time at temperatures of 

 from — '4 to — 1'8° C. were successfully hatched. 



M'lntoshf records a striking instance of the vitality of the demersal eggs 

 of Agonus cataphractus. A small bunch of the eggs of this species, which 

 measure about 17 mm. in diameter, was obtained on October, 1894. In 

 January and February following the eggs were frozen, and they remained so 

 for nearly a month. Yet on the 2nd March some of the embryos were alive 

 and were safely hatched. These eggs had therefore passed an incubation- 

 period of 152 days at least. 



The egg3 of the salmon do not appear to suffer much from the temporary 

 freezing of the water. 



* The temperature of the air at one time during the 12th September was about 15° C. 



t M'Intosh — " Contributions to the Life-Histories of the Food and other Fishes : 

 —4. On the Spawning-period of the Armed Bullhead and the Vitality of its Eggs." 

 Thirteenth Annual Report oj the Fishery Board for Scotland for 1894. Part III. 

 Edinburgh, 1895, p. 230. 



