VALUE OF NOEWEGIAN LAKES FOR FISH CULTURE, 555 



or four years its own weight doubles yearly with the same amount of 

 food; thus, for instance, a trout during the fourth year which at the be- 

 ginning weighs about 0,75 kilogram, consumes about 3G5 times 0.0075= 

 1.85 kilograms, while it will have gained in weight 0,75 kilogram ; the 

 ratio between the food consumed and the increase of weight is also at 

 this age quite particularly more profitable than at a later age, because 

 the increase of weight in the last case bears the proportion to the nour- 

 ishment consumed of 75 to 185, or 1 to 2.4, and in the first case of 2.5 to 

 18.25, or 1 to 7. Even if the increase were the same at this age as earlier, 

 the proportion would become as 5 to 18.25, or as 1 to 3.6, or in a consid- 

 erable degree less profitable tlian in the younger stages. 



One must also strive to catch the older fish as comi^letely as possible, 

 and for this end the spawning time will furnish the best opportunity. 

 Whether one will then eat them or put them into a separate smaller 

 pond, where they will be easy to catch at any time, for i^reserving and 

 feeding them until they are in better condition, is a matter of taste. 

 That fish of prey of other species which possibly may occur ought to be 

 exterminated by all means is self-evident. 



For the attainment of a reasonably large profit it is, moreover, as be- 

 fore mentioned, necessary, in the greatest j^ossible extent, to improve 

 (gjode) the water which is the object of cultivation. This may occur in 

 different ways, depending on how the circumstances may be varied. It 

 applies to the whole circle of creation that the lower organisms live uj)on 

 plants, and in their turn serve as food for the more highly organized 

 flesh-eating animals ; and it is a settled thing that men, by assisting the 

 operation of nature, can, to a very considerable extent, and in many, if 

 even not in all, directions, promote this activity toward a very consider- 

 ably increased production. It will everywhere be in the power of the 

 fish culturist, in the same way as is emj)loyod for the fishes in question, 

 which are the peculiar object of the breeder's care, to promote the hatch- 

 ing of species of fish which feed chiefly on vegetables, in order that sub- 

 sequently, when they have reached the proper development, they may 

 serve as food for the choicer fishes. 



In the same way one may promote the increase of crustaceans and 

 mollusks, which likewise, to a great extent, serve as food for the nobler 

 fishes. It will, moreover, in many places be an easy matter, by the 

 employment of vegetables, which, in comparison with meat, cost little, 

 such as carrots, peas, meal, and potatoes, to feed a greater multitude 

 of the vegetable-eating fishes and other aquatic animals than the waters 

 of themselves could support. Moreover, one can, if the opportunity 

 offers, to a greater or less extent, provide directly for the nourishment 

 and food of the cultivated fish by the use of all kinds of animal offal, 

 the flesh and entrails of all sorts of fish, birds, and four-footed beasts, 

 which have httle or no value.* 



By tlie use of such means, among which cod-roe might, perhaps, be 

 *Mr. Seth Greeu says: "It is more profitable to raise trout than hogs." 



