32 REPORT OF THE COMMISSIONER OF FISHERIES. 
a permanent buoy was placed upon the principal grounds known and 
described as the Beaufort offshore fishing erounds, i in the hope that 
such a mark would aid and stimulate the local fishermen who might 
be without the equipment or the experience to enable them to locate 
such a circumscribed area by methods of navigation. 
THE DISEASES OF FISHES. 
Tt is not generally realized to what extent fishes are subject to 
parasitism and to what degree their existence is contingent upon the 
less obvious factors of environment. Without presenting the con- 
spicuous features of an epidemic, certain of the ever-present parasites 
may so reduce the vitality of individual fishes as to cause them to fall 
an easier prey to voracious enemies. Deleterious chemicals may be 
introduced into the water, not only through evident sources of pollu- 
tion, but through very indirect, unintentional, and ordinarily unob- 
servable means. Furthermore, the effect of the introduction of 
chemicals or of commercial waste products, or of natural débris, 
when it is without direct poisonous effect, may give rise to such 
chemical reactions in the water as to render the environment unsuit- 
able for the support of fish life. 
With the services of temporary investigators at its various labora- 
tories the Bureau has made special efforts to investigate the effects of 
various sorts of pollution, to study the forms and ‘the life histories 
of the different kinds of parasites, and to determine the modes of 
transmission of infection. The general object has been to lay such 
a foundation of familiarity with the facts as to be able to determine 
the means of control. The Bureau receives a large number of re- 
ports and inquiries from the public relating to the occurrence of 
unusual conditions of mortality among the fishes both in private and 
in public waters. Such matters are of proper concern to the Govern- 
ment, and every possible effort has been made to render appropriate 
service. 
In the lack of any permanent assistant qualified in the study of 
such matters, and familiar with the practical conditions involved, 
the Bureau has been seriously hampered in its effort to do justice to 
the demands made upon it. This deficiency will not be felt in the 
future as in the past, since Congress has made provision for the em- 
ployment of a competent assistant to serve as fish pathologist. 
FRESH-WATER MUSSELS. 
The propagation of fresh-water mussels shows continued develop- 
ment. The number of larval mussels planted was 344,655,260, an in- 
crease of 50 per cent over the output of the preceding year. In con- 
nection with the mussel propagation, 32,650 adult and 15,083 finger- 
ling fishes were rescued from overflow ponds. As the result, partly 
of greater efficiency and partly of somewhat more favorable weather 
conditions, the unit cost was still further reduced, being 2.7 cents 
per thousand glochidia planted, as compared with 4. 3 cents per thou- 
sand in 1914 and about 7 cents in 1913. Experiments are also being 
conducted to determine the feasibility of rearing certain valuable 
species of fresh-water mussels in crates or in ponds, and an encour- 
aging degree of success marks the progress of the experiments during 
