SIZE OF EGGS AND EFFECTS OP FREEZrXG. 37 



"wero it believed in and acted npon, would bo disastrous to oui" salmon fislicries ; 

 as it might be advanced that these iishes could breed as well in the ocean as in 

 rivers, consequently no necessity on their behalf arises for keeping our fresh 

 waters pure, or having tree passes in our streams in order to allow them to reach 

 their spawning-beds. It Avas probably from such views the notion of the par 

 being a distinct species sprang, and even now there are some Avho assei't a doubt 

 whether our " last-springs " are the young of Sabiio saliu-.* Willoughby followed 

 Gesnei', and in his lllstorij of Fishes, published in 1G8G, lib. iv, adduced reasons 

 for disputing the correctness of Roudelotius's opinion ; while Pontopj)idan, in 

 1755, in his Natural History of Norway, returned to Rondelctius's view, asserting 

 that ho Avas well assured that salmon chiefly eject their roe at the mouths of 

 rivers, Avhero they empty themselves into the sea, or else a little above the salt 

 water.f 



I thought it well worth making investigations on the point, which was done 

 by placing the ova in tumblers and changing the Avater once daily : for eggs simi- 

 larly placed in tumblers of fresh Avater hatched. Two trout eggs kept in l)rackish 

 water at the specitic gi*avity of 1008'^ (except for two days at 1019") from January 

 9th hatched, one on February 28th the other March 1st, but one had dropsy 

 of the sac, apparently due to the medium in which they had been kept, still as 

 a rule salmonoid eggs placed for a day or two in salt Avater, i.e. of a salinity of 

 1020° and upwards, invariably died, as Avill be fully detailed Avhen discussing 

 " breeding " of salmon and trout. 



Among the many agencies that tend to limit the geographical distribution of 

 these fishes is that of temperature, the Salmonida), with few exce2:)tions, being 

 confined to an area possessing a cold or temperate climate, while the salmon, trout 

 and char deposit their eggs during the winter months. It is a matter of history 

 hoAv Mr. YoulJ first proved that eggs of fishes of this family could be transmitted 

 even to the Antipodes by the agency of cold scientifically utilized, and although 

 some authors have contended that freezing ova will not destroy the life of the 

 embryo, such a contention is most probably incorrect. Dr. John Davy ascertained 

 that impregnated salmon ova are capable of resisting a degree of cold sufficient to 

 freeze water and imbed them in ice ; Avhile in 1881 it was stated that a large 

 amount of salmon eggs in rivers in the highlands of Scotland had been destroyed 

 by frost. 



Circumstances occurred Avhich permitted the eff"ects of freezing fish-eggs to be 

 watched by myself on rather a large scale during the winter of 1885-86§, about 

 10,000 Lochleven trout ova that had been taken from the fish on the 10th, having 

 been sent from Howietoun to Cheltenham and am-iving on December 12th. 

 They were transmitted in water in a swing tin can, suspended to a strong wooden 

 frame, and when received the lid was found to be tightly frozen doAvn, Avhile even 



* A history of this controversy in the British Isles during the present century as regards 

 salmon will be given under the head of the " breeding " of this tish. 



f As bearing on this question of the effect of saline water, I may notice the paper of M. Emilo 

 Young (Ann. and Mag. Nat. Hist., January, 1884, xiii, page 74). " On the influence of Physico- 

 chemical agencies upon the development of the Tadpoles of Rana esculenta." He concluded 

 they were developed the more slowly the greater the degree of salinity of the water. 



J M. Pouchet has given reasons based upon experiments that no vertebrate animal which has 

 been completely frozen is susceptible of resuscitation, owing to the blood having become disorgan- 

 ized, although it has been abundantly proved that fish may be revivified after they have been 

 surrounded by ice without being entirely frozen. Even partially frozen fishes if resuscitated often 

 subsequently succumb from the injury their constitution has sustained. Livingston- Stone (Domesti- 

 cated Trout, p. 158) observed that he has frozen alevins several times so that they wero glued 

 tight on to the ice and could not stir, and in most instances it did not seem to hurt them at all. 



§ In the above instance 2454 eggs were accidently frozen, at least every one of them was 

 imbedded for some time in ice, 565 being quite dead when thawed out, and without 

 enumerating the daily mortality it will be sufficient to give it in periods of ten consecutive days 

 each, and which were as follows : — 89, 45, 173, 09, 199, 121, 193, 197, and the remainder subse- 

 quently succumbed, not a solitary ovum hatching. A small opaque white spot in most instances 

 showed itself, or else a white semi-circle, subsequently the entire egg became opaque. Those which 

 survived the longest or until the embryo became sufficiently forward to be examined, were in every 

 instance found to possess a badly developed head, and very small black eyes, apparently 

 evidencing a want of development in consequence of the injury received from the amount of cold 

 to which they had been subjected. 



