CANADlAy FISHERIES EXPEniTIOy, VJl'rir, 



47 



II. All oil the bottom by the end of an hour, some endeavouring to rise. Same 

 course as previous sample, only slight mortality after eighty hours, until about half 

 died by the end of 142 hours. 



III. Some few suspended after a quarter of an hour, but at the end of an hour all 

 at the bottom. Some few died after the lapse of fourty-six hours, mortality then increas- 

 ing rapidly until all were dead by the end of 138 hours. 



IV. All on the bottom after a quarter of an hour, some trying to work upwards. 

 Some few died after four hours, more after twelve hours, the remainder with irregular 

 pulsation of the heart. After thirty hours, many dead, and by the end of fifty-two 

 hours from the commencement, none were left alive. 



V. Some few died in the course of the first seven hours, and all within thirty-four 

 hours from the start. 



From the result of these experiments we may be justified in supposing that a stay 

 of any duration in brackish water will be detrimental to eggs and young; this will, 

 however, only occur under quite peculiar conditions, and can be of no importance with 

 regard to the open sea. 



Other factors which might be supposed to have some effect upon the development 

 of the ova are: lack of fertilization, action of bacteria, and internal causes (natural 

 death). 



Prof. Apstein has, in his investigations in the Belt Sea and the western Baltic, 

 shown that considerable quantities of dead — or as he considers, unfertilized — ova occur 

 in the plankton samples. In his work above quoted, " Die Yerbreitung der pelagischen 

 Fischeier und Larven in der Beltsee und den angrenzenden Meeresteilen 190S-09," we 

 find the following table for dead ova (p. 231) : — 



These figures, however, appear abnormally high, for it must be remembered that 

 dead ova — at any rate those of cod and plaice — are only exceptionally found suspended 

 in the water, sinking otherwise very soon to the bottom, they would consequently only 

 appear in plankton samples by mere accident. Unfertilized cod eggs may remain 

 suspended for about two days; those of the plaice somewhat longer. 



As to how far unfertilized or dead eggs appear in the samples from the Canadian 

 waters, I am unable to say on the basis of the preserved material; the question would 

 have to be dealt with by means of fresh plankton samples. 



That cod eggs should be subject to " natural death " in any considerable degree 

 is hardly probable; if such were the case, the mortality figures at the hatchery would 

 be far higher than they are. 



When working under normal conditions, solely with a view of obtaining the greatest 

 possible amount of living young, and without regard to what quantity may be lost, 

 the mortality i)ercentage at Flodevigen amounts annually to something like 12 per cent 

 for the entire period of hatching, including unfertilized eggs. 



The figures for the three last years are as follows : — 



Per cent. 



1912 12-5 



litis 13-S 



1914 11-0 



