CANADIAN FISH-EGGS AND LARVJE 



I. INTRODUCTION. 



When Dr. Hjort invited me to undertake the work of dealing with his valuable 

 material of fish eggs and young from the Canadian waters. I was fully aware of the 

 many difficulties which the task would involve. The determination of ova and young^ 

 from a quarter of the globe where many species of fish exist, whose young stages 

 have not been described, is naturally no easy matter, more especially when only 

 prieserved material is available, and it will, as a rule, be obvious from the outset 

 that complete success must be out of the question. The object of the Canadian inves- 

 tigations was, however, principally to ascertain the biological conditions under which 

 the most important species of fish lived and multiplied, so that possible errors in the 

 deterniiiiatiou of some few of the less frecjuently occurring species would be of 

 minor importance. In view of this fact, and with the promise of every assistance 

 from Dr. Hjort and Magister Koefoed, I undertook the task, all difficulties not- 

 withstanding. 



As to how far the determination of species has been successful, it is naturally 

 impossible to say at present; future investigations of the same waters will, in all 

 essentials, make this clear. I have thought it proper, however, here to make a few 

 introductory observations as to eertain i)articular difficulties which may be imagined 

 as having given rise to erroneous determinations. 



The transatlantic literature on the subject being somewhat scanty, I have had 

 recour.ve more especially to descriptions of European species, and it might therefore 

 seem not unlikely that related western forms could have become confused with or 

 mistaken for these; but regarding the young of species found on both sides of the 

 Atlantic, however, and where good descriptions of the .young stages are available, this 

 source of error does not apply. 



A considerable number of forms have been drawn with great accuracy by Mr. 

 Rasmussen. these including both species previously described and drawn, and also 

 other lesser-known species. I have not thought it advisable to give any description of 

 such forms on the basis of the preserved material, more especially since this would 

 lie outside the scope of the present work. 



As regards the determination of the ova, this is naturally more or less uncertain, 

 since the eggs of many species are indistinguishable one from another until tlie 

 embryos are well developed. In some few cases, on the other hand, the ova may be 

 accurately determined from the time of spawning. It will, moreover, be justifiable to 

 presuppose relation between ova of like appearance in one and the same sample, where 

 some are newly spawned and others with the embryo sufficiently developed to permit 

 of certain determination. 



The present material of ova and young was collected by means of a silk net (In?. 

 diameter) and preserved in 4" per cent formol. The duration of the surface haul.>^ 

 varied somewhat, as a rule between ten and fifteen minutes; the depths, as stated for- 

 tlie vertical hauls, are also in some cases only approximately correct, owing to diffi- 

 culties in the working of the net. 



Similarly, the records as to quantity should not be taken too strictly, these being 

 for like reasons only approximate figures. The proportional quantitative values, how- 

 ever, as between eggs at different stages of development, may be taken as fairly 

 reliable. 



Or).'")l— IJ 



