568 KEPOET OF THE COMMISSIONER OF FISHERIES. 



contains a great deal of nutritive material for the fish, this does not 

 dismiss the Avhole question of vegetable food, as Nicklas implies; and 

 while he says that carp can be raised in ponds which contain but few 

 plants, being fed, I suppose, on animal food, on the other hand 1 have 

 seen ponds in northern Ohio, where carp were retained from spring- 

 to fall, which contained practically no natural food at all, the water 

 being supplied from artesian wells, and where the fish were fed 

 exclusively on corn, barley, etc., and young '"sowed corn," the plants 

 being cut when 1 to 2 feet high and thrown into the pond. I am 

 not prepared to say that these fish grew as rapidly as the}" would have 

 if fed according to Nicklas's formuhe. But this docs not concern us 

 here. The important point is that carp can live vGvy largely, if^ not 

 entireh", on vegetable materials, and that under natural conditions in 

 our open waters plants and plant j)roducts form a ver}- large share of 

 their food. The bearings of this, from an economic standpoint, will 

 be discussed later on, where will also be considered the question of the 

 extent to which carp may be injurious to the spawn and young of 

 other lish. 



Susta maintained that of its own choice carp would first select animal 

 food, a contention in which he v>'as supported b}' the observations of 

 A. Fritsch in Prag and Emil Walter in Trachenberg. Karl Knauthe 

 pointed out that these investigators had used exclusively the highly 

 cultiA^ated races, to which belong the so called Galician and Bohemian 

 carp. He himself extended the investigation b}' comparing as to 

 intestinal contents examples of the old Silesian carp and a new race of 

 it bred by Groger in Lauterbach with examples of the two quick- 

 growing races mentioned above, using for the purpose fish of the same 

 age. These fish, after each individual had been marked so that the 

 four races could not be confused, were placed all in the same pool, 

 which was rich in animal and vegetable food. In this way it was 

 shown that the stomachs of the Galician and Bohemian carp were 

 generally filled with small Crustacea — chiefly Daphn/'a and Cyclops — 

 as long as these were abundant, while insects and their larvae were 

 second onh^, in about the proportion of 3 to 1. Plant food was present 

 onlv as it was taken incidentally with the other. In the cultivated 

 Silesian carp the proportion of animal to plant food was al)out the 

 same. The old Silesian " Bauernkarpfen," however, contained a great 

 preponderance of vegetable materials, such as alga?, diatoms, plant 

 debris, and the seeds of higher plants, and only a few animals, mostly 

 small Crustacea. As soon as the supply of lower animals in the pool 

 was exhausted it became necessarj^ for the Galician and Bohemian carp 

 to adopt a vegetable diet as well. Moreover, Knauthe found the 

 stomachs of these carp filled with a small species of pond snail which 

 \vas abundant in the pool, and which both of the Silesian races spurned. 

 From such and similar researches of Knauthe's it was shown that in 



