330 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



the eggs annually produced by the innumerable individuals to which the 

 Gironde affords protection would hatch out, and if also the waters of 

 the river contained sufficient food to nourish them, the adjacent portions 

 of the sea would soon be tilled up. The causes of the destruction are 

 numerous and powerful, for the crop of fry is always abundant, and 

 either in consequence of inclemeut weather or during high winds, tem- 

 pestuous waves disperse and destroy the legions of larvae which are in 

 process of incubation. Now, the methods which we extol would enable 

 us to escape some of these evils, and would assure those who put them 

 in practice of a certain crop, by protecting the fry from the fluctuations 

 of the temperature, and by this means persisting bad weather would 

 not compromise the regular abundance. 



We have already remarked that it is not a siugle crop of fry which 

 we have each year, but two, and perhaps three. In fact, the season 

 for the fry lasts for at least three months. This interval is sufficient, 

 we have learned with certainty, at Verdon, to permit us to place the 

 collectors three times in the same claire, when the fry will adhere each 

 time. 



The localities adapted for the hatching establishments are not want- 

 ing; they are to be found near the mouths of most of our rivers. Two 

 conditions only are necessary: the waters should be brackish and have 

 a specitic gravity of 1.014 to 1.020, and be readily renewed. 



Perhaps it would serve us much better to show up the advantages of 

 our system by borrowing some data from fluvial fish-culture. 



We know with what success we now treat the eggs of fishes by 

 methods of artificial fertilization, of which M. Coste determined and 

 stated the laws. The cause of the depopulation of the waters is the 

 want of proper economy; and it may be said that in every European 

 state the question of fish-culture is the order of the day, and takes the 

 first rank amongst those economical questions claiming prompt solution. 

 To this end special laboratories for the practice of fish-culture have 

 been established in Switzerland, Germany, England, Russia, Norway, 

 etc. Artificial fertilization is the raison (Vetre, and is the basis of their 

 operations. These have given results much superior to those which 

 are obtained by allowing nature to have her own way. For example, 

 of 1,000 eggs fertilized artificially and cared for in hatching boxes, 980 

 hatch perfectly, while of those left to themselves in the open waters it 

 is estimated that 90 per centum are lost. 



We admit that the eggs of the salmonoids are much better adapted, 

 on account of their large size, to artificial treatment, than those of 

 Ostrco angulata; but even if this comparison is hardly fair, the dimin- 

 ished losses which would result from the application of artificial 



centimetres. There, are consequently about 20,000,000 eggs discharged anuually by 

 an oyster three to lour years old. 



In the ease of the common oyster (O. edulis) this number is reduced to 1,200,000 to 

 1,500,000 eggs. 



