SALMON OVA. 63 



nihilating the whole race by mill weirs, navigation 

 weirs, dams, dykes, and fixed engines. These natural 

 as well as artificial obstructions may be removed or 

 overcome by ladders, yet it requires skill, capital, and 

 time to develop and cultivate the productive powers 

 of any river ; but it is indispensable that the breeding- 

 grounds should be made accessible to the salmon from 

 its sources to the sea. 



We have no means of destroying the natural ene- 

 mies of the salmon in the sea, but in the fresh water 

 we can increase the salmon by protection and care, or 

 we may destroy them by capture. Over the insect 

 tribe in the rivers we have no control, and even if we 

 had it would be unwise to interfere with them, as 

 their larvaB, as well as the insects themselves, are the 

 principal food of young fish; but we may suppose 

 that far more of the ova of the genus salmo are de- 

 stroyed by insects than by all their other enemies put 

 together. 



The trout, the pike, the otter, and fowls are also 

 very destructive, but the dragon-fly and a vast quan- 

 tity of other flies drop their eggs during the summer 

 on the water; these eggs ultimately become the most 

 deadly foe of the salmon by devouring (in their ad- 

 vanced stages of development) millions of salmon 

 ova, assisted by water-beetles and numerous other 

 insects. 



Is it possible to overcome these difficulties by any 

 other means than by artificial propagation? And if 

 not by what means are we to procure the requisite 

 ova, and rear the fish in sufficient quantities for 

 fifteen months ? If this system cannot be carried 

 into effect practically and profitably, then we have no 

 other left but the efficient protection of our rivers by 

 clearing them of destructive pollutions and affording 

 a free passage for the fish from the sources of the 

 rivers to the sea. 



