36 NATURAL HISTORY OF THE SALMON. 



From these experiments, we may see the ne- 

 cessity of having the gravel free from the eggs 

 of grubs and larvae of insects, and likewise learn 

 the great destruction of ova that takes place by 

 their means in the beds of all our rivers and 

 streams. It is true that insects, in all their stages, 

 become, in their turn, the chief food of the young 

 fish, and that no river could feed or support fish, 

 if these were absent; but as the fry of the salmon, 

 at least, require no external nourishment (as we 

 shall show afterwards) for the period of six weeks 

 after hatching, the insects can be of no use to 

 them for food, and, in artificial rearing, food is 

 supplied them by their keeper. There is little 

 doubt but that the most of our salmon rivers 

 (if well protected) would be sufficiently stocked 

 with fish, if they were not, in every instance, 

 over-fished by nets of all kinds ; but when that 

 is the case, artificial rearing, if generally adopted 

 on a scale sufficiently large for the size of the 

 river, would rescue enough of the ova from their 

 enemies to meet this extra fishing. 



AETIFICIAL SPAWNING OF THE SALMON 

 SPAWNING OF 1853. 



On the 23d of November, 1853, this operation 



