WATER CULTURE COMPARED WITH LAND CULTURE. 237 



young of the larger, and becoming, in their turn, a prey to those 

 of maturer growth. And here is the true explanation of the rapid 

 extinction of fisheries when they become depleted beyond a cer- 

 tain limit. Nature balanced the number of each kind, providing 

 that mutual destruction of one another should keep all in check. 

 Man destroys this equipoise by killing those only that he can use. 

 The rest then augment at an increased ratio, the enemies of all 

 sorts of the edible kinds have no check, they multiply, and multi- 

 ply until they obtain the mastery, and then quickly comes the end 

 when the better sorts are exterminated. This is apparent, and is 

 sustained by the fact that new varieties when introduced into 

 unaccustomed waters increase for the first few years with inordi- 

 nate rapidity. For a time their natural foes do not exist in suffi- 

 cient numbers to curtail this growth, but as the latter develop the 

 counterbalance is restored and the stimulated activity of reproduc- 

 tion ceases. 



The time may come in the distant future when the edible fishes 

 shall be made so abundant by artificial cultivation that the food of 

 the piscivorous sorts may fail ; then it may be necessary to breed 

 those which live on water-grasses and vegetables to supply the 

 others with sustenanee. At present, however, there is no such 

 necessity ; not only is the sea alive with food, but the large lakes 

 are .equally well peopled. It is a curious fact that in Lakes LTuron 

 and Superior is found the salt water shrimp in the deeper parts, 

 and in quantities equal to that in the ocean. The shrimp, which 

 itself is exceedingly prolific, is the principal food of the true 

 salmon, the salmo salar, and is supposed to constitute the red 

 color of the flesh. But if it were requisite the cyprinidae could 

 be cultivated or introduced, or some other variety which lives 

 solely on a vegetable diet, but which of themselves are not good 

 for food. This will doubtless be done as soon as it is needed, and 

 has already been successfully tried in Europe, so that should the 

 present supply of fish food give out it could be replenished. 



The fisheries of our coast are among the most valuable commer- 

 cial interests of our country. Millions of money are invested 

 and hundreds of thousands of men are employed, while the food 

 thus obtained is a large per centage of the total supply of the 

 eastern markets. Not only is the profit of this business a matter 

 of general advantage, but the residents along the eastern bays 

 and lagoons and upon the larger rivers derive their principal 

 means of sustenance directly from these waters, and in all these 



