REPORT OF THE COMMISSIONER OF FISHERIES. 
15 
the sponges; enough, however, is known to justify the belief that 
under proper state regulation and protection very important eco- 
nomic results must come from utilization of barren grounds for 
sponge planting, while at the same time the stability of the sponge 
crop will be assured. 
STUDY OF FISH DISEASES. 
The Bureau has continued to give attention to the diseases to which 
fish, particularly when under domestication, are liable, and during 
the past year has devoted special consideration to the occurrence of 
cancers and other tumorous growths. Tumors in fish have been 
known for many years, and the Bureau has from time to time col- 
lected specimens of various kinds of tumors from different species of 
fish. Owing to the activity that has characterized the investigation 
of cancer during the past ten years, cancer in the lower animals, and 
in fact in all the vertebrates, becomes a subject of great interest. 
Certain types of cancer appear to be more frequent than others in 
domesticated fish ; and cancer of the thyroid gland has been observed 
at various times in trout and salmon at government and other hatch- 
eries. Of late the disease seems to be on the increase, and the Bureau 
has undertaken a thorough and systematic investigation of the entire 
subject of cancer in fish, and to this end has availed itself of the serv- 
ices of the director of the New York State Cancer Laboratory, who 
will pursue his studies in conjunction with the regular work of that 
institution. The Forest, Fish, and Game Commission of the State 
of New York also will cooperate in this work. 
The inquiries already made have shown that the subject is very 
important and will require thorough study covering a considerable 
period of time. Careful investigation has been made in two localities 
where the disease is so prevalent as to constitute an epidemic; and 
the work will be extended so as to include a systematic examination 
of wild fish in open waters as well as the young and adult fish in gov- 
ernment, state, and private hatcheries. At Buffalo, N. Y., where it 
is proposed to conduct experiments on fishes, arrangements have 
been made for the installation of two aquaria on the closed-circulation 
plan, with full provision for refrigeration and aeration of the water. 
The Bureau is fully alive to the far-reaching importance of this in- 
vestigation, and will devote every energy and facility at its disposal 
for the prompt and thorough elucidation of the problems of the cause 
and prevention of this most serious malady. 
OTHER INQUIRIES AND EXPERIMENTS. 
It has long been a mooted question whether the steelhead trout 
and the rainbow trout are different species or the same species with 
somewhat different habits. A special study of these fish in their 
home waters has been undertaken. The evidence thus far obtained 
points to the specific identity of the fish. The question is not without 
