REPORT OF THE COMMISSIONER OF FISHERIES. 43 
ters of fish culture, there is as yet too little serious endeavor to find 
real causes or to apply appropriate remedies. Year by year the 
Bureau is devoting more careful and fitting attention to the prob- 
lems of fresh-water fisheries, and some of its principal activities in 
this field may be referred to. 
The problem of fish culture, at least as referring to pond fishes, 
is primarily ofe of food supply. Our knowledge of the food of 
fishes is as yet seriously inadequate. The food taken by fishes 
varies with the species, with size and age of the fish, with the season 
of the year, and with the abundance of the various kinds of food 
materials present in different bodies of water. A few observations 
in one locality or at one season of the year afford no criterion for 
the conclusions that we may seek to draw, for an appraisal of the pos- 
sibilities of fish production in any body of water, for an understand- 
ing of the variations in the sizes attained by a given species of fish 
in different bodies of water, and for the direction of our efforts to 
promote an abundent and reasonably constant supply of food under 
all conditions subject to control. 
One of the investigations of the food of fishes that has been pur- 
sued comprises an examination of a number of perch taken from 
, each of two lakes in Wisconsin during each week in the year. At 
the same time collateral studies have been made of the food of many 
of the important fishes, their habits and interrelations. Some of the 
results have been submitted for publication, while other reports are 
in preparation. The accumulation of such data is not of theoretical 
interest; it is indispensable to a purpose, for it must lead eventually 
to intelligent conclusions as to the highest possibilities in rearing 
fishes ahi the methods of realizing such possibilities. 
At the Fairport station several special fish-food studies are being 
actively pursued. In connection with the experiments in rearing 
buffalofishes, examinations are systematically made to determine the 
food taken at all sizes and all stages. Investigation of the food of 
all small fishes in the experimental ponds are being conducted in 
connection with parallel studies of the available foods in the ponds. 
Systematic studies are being made of the aquatic insect life. Experi- 
ments are also being directed at the problem of promoting an abund- 
ant growth of food organisms by methods of fertilizing the water or 
otherwise. 
The investigation of the habits and movements of fishes in the 
Mississippi River with especial reference to the obstruction of the 
river by the dam at Keokuk has been continued throughout the fiscal 
year. Only tentative conclusions have as yet been reached, but the 
progress of the investigation has been such that it may be hoped to 
present a full report within another year. 
Within the year there has been completed a report embodying the 
results of an earlier investigation of the Rangeley Lakes of Maine. 
These have for many years been among the more widely known for 
their game fishes, and the investigation was undertaken to gain 
information that might serve not only as a guide to fish-cultural 
lan vamath of these particular waters but as a basis for the adop- 
tion of a proper policy with regard to other lakes. The report 
comprises an unusual body of information regarding the habits and 
relations of many important food and game fishes. 
