REPORT OF THE COMMISSIONER OF FISHERIES. 23 
forms of plant life. Such investigations are of fundamental import- 
ance because all food of fish is provided through the medium of 
plants. There can be no fish or animal life except as the inorganic 
materials are converted by green plants into materials that are suit- 
able for the food of animals. Fish are thus dependent upon plant 
life whether they forage directly upon the plants or subsist upon 
smaller animals that derive their food directly or indirectly from the 
vegetation. But some plants are more useful than others, and some 
are undoubtedly injurious in their effects upon ponds. It is neces- 
sary, therefore, that previous knowledge be obtained regarding the 
biological and economic relations of the various forms of plant life 
within the fish pond. 
A significant anatomical study of the salmon, conducted princi- 
pally in the Washington laboratory, has brought to light previously 
unrecognized facts regarding the structure of the reproductive or- 
gans and the normal manner of extrusion of the eggs. These facts 
are found to have a direct bearing upon fish-cultural practices, and 
they dictate the necessity for certain changes in method and for ex- 
treme care in the handling and stripping of spawning trout and 
eastern salmon in order that the loss of eggs and permanent injury 
to the breeding fish may be avoided. 
Reference may be made to an investigation of the possibility of 
utilizing the abandoned rice fields of South Carolina and Georgia 
for the culture of carp on a commercial scale. 
INVESTIGATIONS AND PRACTICAL WORK IN ANTIMALARIAL CAMPAIGNS. 
With the measures which are generally relied upon for the control 
of the abundance of mosquitoes and the eradication of malaria, this 
Bureau has no direct concern. They lie within the domain of sani- 
tation and entomology. It may be said, however, that it has become 
very clear to all concerned that under many conditions the direct 
methods of sanitary science generally employed in combating the 
mosquito, whether physical, chemical, or engineering, either are not 
practicable of application, or else, when applied, fail of accomplish- 
ing the desired purpose. It has been found necessary in many cases 
to rely to a great extent upon nature’s method of controlling the 
abundance of organisms through their competitors and enemies. It 
is well known, however, that nature’s control of the abundance of 
mosquitoes, as of other animals and plants generally, is relative and 
not absolute. The problem in this case is to find means of making 
the enemies of mosquito larve dominant over their natural prey, of 
making them efficient in the extermination of the larve of anophelid 
mosquitoes at least. 
The problem is primarily within the domain of aquatic biology 
and concerns especially the small mosquito-eating fishes and other 
associates; and in this problem, in its phases both of investigation 
and of practical work, the assistance of the Bureau of Fisheries has 
unio by the Bureau of Entomology and the Public Health 
ervice. 
The cooperation with the Public Health Service has been prin- 
cipally in the urgent task of protecting the health of soldiers in one 
of the large southern cantonments. The plan of work comprised 
