50 THE NATURAL HISTORY AND HABITS 



The German trout also take a much shorter time to 

 hatch than they do in this country. For Mr. Jacob! 



number of fish that spawn there annually at 30,000; viz., 15,000 

 males and 15,000 females. He says: "To each of these I 

 assign an average weight of 10 Ibs.; this being the usual average 

 ascribed to a Tay fish. A ten-pound breeder, it has been ascer- 

 tained, yields about 10,000 ova certainly not fewer conse- 

 quently the number of ova cast in the spawning season on the 

 various breeding grounds referred to may be computed at 

 150,000,000. How much of this large amount of spawn are we 

 entitled to suppose is brought to life, becomes distributed over the 

 rearing ground, attains the smolt size, and, assuming its plumage, 

 eventually finds its way to the sea or firth? The hazard to which 

 these 150,000,000 pellets are subjected may be described as fol- 

 lows : 



First. In every wain there are what are known as the barren 

 ova; in other words, there are pellets on which the effusion of 

 the milt has no effect; these, however, in general form a very 

 small fraction of the deposit, not more than a hundredth part; 

 the detriment, in fact, accruing from this source is so trivial as 

 scarcely to deserve notice. 



Secondly. There is a surface loss I mean by this the loss of 

 that portion of the ova which escapes from the fish without being 

 covered up consequently it is carried onward by the current, 

 and becomes the prey of trout, eels, water ouzels, &c. Under 

 the same head may be included so much of the deposit as hap- 

 pens to be inefficiently ploughed in; and I may add, also, the 

 contents of redds formed upon the side water or extreme shallows 

 which are exposed to draughts before the hatching time. These 

 casualties alone very seriously affect the ova, and reduce them, in 

 all probability, to one third of the original amount. The insinu- 

 ating quality attributed by eminent naturalists to the milt does 

 not permit me to affirm that any one pellet on the natural bed 

 escapes contact with the inoculating fluid; I therefore abstain 

 from concluding that the deposit is in any respect damaged for 

 want of the material requisite to preserve or vitilate it. 



A third casualty to which the spawn becomes exposed takes 

 place immediately on their being hatched, or while the process of 

 hatching, which occupies several days, is going on ; then it is 

 during the consumption of the vitelline bag, that the common 

 trout commits its most serious depredations, being in a hungry 



