PROGRESS IN BIOLOGICAL INQUIRIES, 1926 673 
comparatively small areas, you will see that the opportunity for the spreading 
of various diseases, which under natural conditions usually cause little injury, 
becomes an important factor. The most serious disease we have to deal with 
in the case of the young fingerling is caused by a protozoan—a flagellate—which 
in certain stages of the life cycle attacks the epitheliai lining of the intestine 
and causes extensive destruction of the epithelial walls. Death of the host 
quickly follows. In another stage it lives as a free-swimming flagellate in the 
lumen of the intestine. In this stage it causes very serious effects. The host 
first becomes emaciated, growth is stunted, and it gradually becomes weaker 
and weaker, and eventually may die. I have often wondered how they could 
stand such a severe infestation without showing more serious effects than 
they do. Sometimes the entire contents of the intestine appear as a writhing 
mass of these organisms. 
Last summer at the Holden a ition we discovered two new diseases—one 
a gill disease, due to bacteria, which appear on the surface of the gill. The 
long filamentous bacteria are found lying side by side in a continuous layer, so 
as to form a film over the gills. As a result of the irritation produced by the 
bacteria, the epithelial membrance becomes thickened and the adjoining fila- 
ments may fuse into a common mass. Of course, as a result of this thickening 
of the epithelium and the bacterial film covering the gills, the intake of oxygen 
through the gills is interferred with seriously, even if there are no other detri- 
mental effects. The disease may cause heavy mortality. It has been found 
that it can be controlled easily by using a solution of copper sulphate, which 
is very effective in many diseases of this character. 
The other disease to which I have referred affects only the fins. This, again, 
is probably a bacterial disease, though our investigations in this case are not 
so far advanced. It probably can be controlled by copper sulphate solution, as 
in the case of the disease that attacks the gills. One of the great difficulties 
in studying diseases at hatcheries is that usually we do not find out about them 
until they are far advanced. By the time the mortalities become heavy enough 
to attract the attention of the fish-culturists the diseases are so far advanced 
that most of the fish die. We should be able to recognize these diseases in the 
early stages. I think we can make better progress in controlling these diseases 
by thorough study of them at Holden than by relying on reports received from 
superintendents of the hatcheries. I might also say in this connection that it 
is our purpose at this hatchery not to run it in a purely experimental manner. 
What we hope to do is to conduct it in much the same way as is followed at 
the other hatcheries—crowd the fish, etc. We are developing a practical hatch- 
ery, with thousands of fish, such as we have in various Federal and State hatch- 
eries. In this way (reproducing hatchery conditions) we shall get a picture 
of what goes on at the hatcheries throughout the country. 
Another line cf investigation is the method of handling the fish. We have 
not attempted much in this field, other than to carry on some experiments as 
to the effects of light on fish. Results indicate that it is better to protect 
young trout from exposure to direct sunlight. Mr. James will tell you more 
about this experiment. 
Another problem on which we are just beginning is that of selective breeding. 
The more I think of it, the more I wonder why it was not taken up long ago. 
There are great possibilities in this direction. The Japanese and Chinese have 
been doing it for some time with goldfish. There is no doubt but that trout 
that have been reared in the hatchery for several generations are often more 
adaptable to hatchery conditions than are the wild fish, and that undoubtedly 
is due to more or less selective breeding, which is inseparable from ordinary 
hatchery practices. We are confining our breeding experiments to brook trout. 
What we are trying to do is to get a strain of trout that will grow rapidly and 
mature early, producing the maximum number of eggs. Later on, we hope to 
extend the work to other species. 
Another problem that we are attempting to investigate, but on which we 
have not made much progress, is to determine the survival of the fish from 
the hatchery when planted in streams. This can be correlated closely with 
another problem—the best age at which to plant trout. This is a perennial 
problem that has been cropping up for years. No two fish-culturists have the 
same idea on the subject. The questions revolve around this one point—what 
is the proper size or age at which to plant trout? As I see it, it is purely a 
business problem and perhaps can be expressed in another way; that is, how 
can you produce 1,000 fish in a stream, above the legal size, with the least 
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