OUR RIVER HARVESTS. 281 



gooseberry. All such eggs must be removed from the 

 water, or they would otherwise taint its purity ; and as 

 the increased bulk renders them lighter than the 

 element in which they lie, they float to the surface and 

 are readily detected. 



Whether the eggs are hatched sooner in the arti- 

 ficially made gravel beds of the troughs than in the 

 natural gravel of the river is not very clear, but it is 

 certain that even in the open-air boxes, where all con- 

 ditions are apparently identical, the salmon eggs are 

 hatched in little more than half the time which the 

 generality of books mention as necessary for that opera- 

 tion. It is hardly needful to say that the rapidity of 

 hatching is an important element in pisciculture, and 

 that the breeding apparatus is rendered more valuable 

 in proportion to the number of hatchings of different 

 fish it can turn out in a season. After each hatching it 

 is as well to remove the gravel, wash the troughs 

 thoroughly, and not to replace the stones and gravel 

 until they have again been submitted to the ordeal of 

 boiling water. 



The question of mixed or hybrid breeds is now 

 attracting considerable attention, and many thoughtful 

 inquirers are endeavouring to produce mixed breeds of 

 fish just as enterprising agriculturists produce breeds of 

 cattle. It seems to have been tolerably well proved 

 that with trout the surest method of obtaining the 

 heaviest and finest fish is to introduce continual addi- 

 tions of new blood into the establishment, so that the 



