220 AMERICAN ANGLER'S BOOK. 



deposition, the specific gravity of the water is less than that 

 of the mature spawn, for the grains of ova fall to the bottom 

 like grains of shot, and the milt sinks, as if it were molten 

 lead. However, we must take into account the effect of the 

 force by which ova and milt are expelled downwards by the 

 spawning fish. 



" As some of the ova are deposited and impregnated ten or 

 more days sooner than other portions, we must expect to see 

 the incubating process completed by degrees. Such, in fact, 

 is the case. The evolving of the fish foetus is not simultane- 

 ous, but gradual, and the infant fry come out from their sand- 

 bed by degrees ; at intervals of time corresponding with the 

 intervals that took place during the deposition of the ova. 

 "We may, therefore, have young fish, from one and the same 

 nest, differing in age from one to ten or fourteen days. 



" The length of time necessary for the completion of the 

 incubating process varies according to the localities of rivers, 

 because locality produces different temperatures. The tem- 

 perature of river-water is also very sensibly affected — 

 heightened or diminished by the mildness or rigor of the 

 season. In the rivers of the north of Scotland Salmon ova 

 are hatched in a period varying in duration from one hundred 

 to one hundred and forty days. In conformity with the 

 habits of oviparous, or egg, or spawn-bearing fish, the parent 

 Salmon having deposited their spawn, impregnated it, and 

 covered it in beneath sand and gravel, take no further heed 

 of it, or the fry it produces, except, perchance, hereafter to 

 feed upon them. Water influenced by atmospheric action is 

 the sole incubating agent. I may here observe that after the 

 ova are covered in they are safe from all casualties, on which 

 point more hereafter. 



" It is during the deposition of ova that they are destroyed, 

 and the great destroyers of them are river Trout of every 



