164 BULLETIN OF THE BUREAU OF FISHERIES. 



others together." It is true, of course, that there is a very marked difference in the 

 rate of growth of trout, even under apparently the same food conditions. Trout 

 culturists, for instance, find it necessary to sort the young trout of a pond at regular 

 intervals after the3 T are a few months old, and separate the larger, precocious 

 individuals from the smaller, weaker ones, in order to keep the former from preying 

 upon the latter. But, in spite of this apparent contradictory evidence, there is little 

 doubt that the great difference in the results obtained in the above experiment was 

 due, in some measure at least, to the different kinds of food supplied. 



As long ago as 1653 Walton appreciated the importance of the quality of the feed- 

 ing ground, for he says: "And certainly, as some pastures breed larger sheep, so do 

 some rivers, by reason of the ground over which they flow, breed larger trouts." 

 Francis (1868) makes the assertion that "trout in one stream will be much larger, 

 firmer, redder, and better shaped than in others. This may. in a measure, be owing 

 to the greater abundance of food, but I have every reason to believe that it proceeds 

 quite as much from the kind of food that they are enabled to obtain." Further on 

 he says: "In lakes also it is a very common thing to find the trout in one lake large, 

 blight, and well fed and in another, very similar in appearance and perhaps only a 

 bare half mile distant from the other, they will be long, black, and lean, with heads 

 out of all proportion to the thickness of the body. In another, probably hut a 

 similar distance from the first two, the trout will be abundant, but very small, though 

 bright and well colored." To exemplify this he cites a group of small lakes in which 

 he had fished and attributes the superior condition of the trout in the smallest lake of 

 the group to the abundance and greater variety of the food found in it. Bah'd (1857) 

 cites a similar difference between the trout of two streams, one of which is a tributary 

 of the other, and he ascribes it to the great difference in the quantity and variety of 

 the fish food which he found in the two waters. 



Thus it is evident that a knowledge of both the quantity and kinds of food found 

 in a stream or lake is of very great importance when it comes to the question of trout 

 culture. This, doubtless, is true also of the culture of all other fishes, and this 

 knowledge would be very valuable in the introduction of a species of fish into new 

 waters. If we know the kind of food on which the fish thrives best and if we also 

 know the quantity and kinds of food available in the water to be stocked, then the 

 problem of stocking the water can be attacked in such a way as greatly to increase 

 the chances of success. Until such knowledge is acquired we must continue to 

 experiment more oi - less blindly. 



FOOD OF THE TROUTS. 



Walton tells us that the trout "lies at watch for any fly or minnow that conies 

 near him; and he especially loves the May-fly." In the two and a half centuries 

 since Walton wrote, relatively little has been added to his observations on the feeding 

 habits of most of the trouts, though several writers, especially writers on trout-culture, 

 have commented in a general way upon the great variety of trout food. There is 

 very little definite information as to the quantities and proportions of the various 

 component elements, however. From general statements we learn that the food 

 includes various kindsof worms, all kindsof insects (both adults and larvae), mollusks 

 of one sort or another, crustaceans, small lish, fish eggs — in fact, almost anything 



