568 REPORT OF THE COMMISSIONER OF FISHERIES. 
contains a great deal of nutritive material for the fish, this does not 
dismiss the whole 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 I 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 they would have 
if fed according to Nicklas’s formule. But this does not concern us 
here. The important point is that carp can live very largely, if not 
entirely, on vegetable materials, and that under natural conditions in 
our open waters plants and plant products form a very 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 fish. 
Susta maintained that of its own choice carp would first select animal 
food, a contention in which he was supported by the observations of 
A. Fritsch in Prag and Emil Walter in Trachenberg. Karl Knauthe 
pointed out that these investigators had used exclusively the highly 
cultivated races, te which belong the so called Galician and Bohemian 
carp. He himself extended the investigation by comparing as to 
intestinal contents examples of the old Silesian carp and a new race of 
it bred by Gréger 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—chiefiy Daphnia and Cyclops— 
as long as these were abundant, while insects and their larvee were 
second only, in about the proportion of 3to1. Plant food was present 
only as it was taken incidentally with the other. In the cultivated 
Silesian carp the proportion of animal to plant food was about the 
same. The old Silesian ‘‘ Bauernkarpfen,” however, contained a great 
preponderance of vegetable materials, such as alge, diatoms, plant 
débris, and the seeds of higher plants, and only a few animals, mosily 
small crustacea. As soon as the supply of lower animals in the pool 
was exhausted it became necessary 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 
was 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 
