2/6 Roosevelt Wild Life Bulletin 



observer, without any consideration of past or present conditions 

 other than those immediately observed, i. e., the decrease in size 

 or in number of the fish. Usually, even when the deterioration in 

 size and decrease in numbers are concerned, the explanation of the 

 one fact is in no way related to that of the other. Deterioration in 

 size has often been attributed to " inbreeding,'' whatever is meant by 

 that term in connection with such cases. The remedy usually recom- 

 mended has been *' new blood." In such explanations, presumably 

 " inbreeding "' signifies that the fish have become physically and 

 physiological!}" " run down " from breeding in comparatively limited 

 numbers. But it does not appear to be recognized that fish have 

 naturally existed for years in some waters and bred together in 

 even smaller numbers without deterioration and that in some other 

 localities fish have actually increased in size as the number declined. 



In " Modern Fish Culture," Mather ('oo) says that with fowls 

 and the cattle on the farm there is danger of inbreeding because the 

 parents, especially the sires, are so few. But he adds, " There was 

 no such danger among the herds of buffalo and there is none among 

 the trout in confinement. Take the eggs from 2,000 fish and fertilize 

 them with the milt of i ,000 males ; turn the progeny loose and breed 

 from them two years later, and what are the chances of mating 

 brother and sister?" 



The migration view seldom is supported by any evidence, nor is 

 any reason suggested as to why after residing in a lake for a number 

 of years, the fish should finally decide to change their abode. Such 

 an explanation is particularly illogical when applied to the decrease 

 of indigenous fish which have existed in a lake for untold years. 

 The commonly accepted view that indigenous fish permanently 

 vacate a lake or stream, has led to the unnecessary and therefore 

 wasteful expense in the erection of screens in an effort to prevent 

 the migration. 



Undoubtedly when possible, fish will leave unfavorable for more 

 favorable conditions. This fact simply emphasizes the necessity of 

 ascertaining the conditions before introductions are made. 



That the decrease in numbers of fish may be attributed to their 

 having Ijeen devoured or destroyed 1)y one or another natural enemy, 

 when such enemies are present in the same body of water, is an 

 explanation which it is claimed, is based upon known facts. But in 

 many cases in question the facts have not been verified. 



It is known, for example, that pickerel subsist largely upon fish 

 and that they have always been adjudged as notoriously ravenous. 

 When a bodv of water once containing ]x)th trout and pickerel has 

 become depleted of trout the pickerel is accused of being the direct 

 cause of the depletion. A'^ery often the depletion of trout may be 

 more justlv attributed to the greed of man than to the voracity of 

 pickerel. X'oracity is characteristic of all predator}- fishes, and in 

 the case of fish-eating fish " voracity " is a relative term, much 

 depending upon the size of the fish and its opportunitx to displa}' 

 that characteristic. 



