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BULLETIN OF THE BUREAU OF FISHERIES. 
The occurrence of cancer in the lower animals has been frequently noted of late years, and it is by 
no means so rare among them as it was at one time thought to be. I have, however, been unable to 
find any mention of it having been noted in fish. 
A report on this disease in trout appeared in 1902 in the General Fisheries Magazine 
(German), by Marianne Plehn, who recognized it as a disease of the thyroid gland. 
L. Pick reported fully on the subject in a paper entitled “Carcinoma of the Thyroid in 
the Salmonidae,” describing 10 fish affected with the disease, which, in agreement with 
all other authorities, he concludes, is genuine cancer. He refers especially to the 
epidemics of the disease, descriptions of which are found below. 
In the reports of the New Zealand Department of Agriculture, Division of Veterinary 
Science, 1901-2, is a report by Gilruth entitled “Epithelioma Affecting the Branchial 
Arches of Salmon and Trout.’’ Gilruth describes a specimen, a 5-year-old salmon {Salmo 
salar) from the Clinton ponds, which had a growth on the third branchial arch and “its 
gill ray.’’ It was the first specimen which had been found there. His description is as 
follows : 
Macroscopical examination. — Growth appeared about the size of a marble, situated oa the center of 
the third branchial arch, affecting laterally the first and third and implicating the branchiae. The 
gill cleft was distended, but until forcibly opened the tumor was not visible. 
Later he received three rainbow trout (Salmo irideus). 
In each specimen the tumor was about the size of a large walnut projecting on both sides of the gill 
cleft. (Fig. 3.) Each tumor appeared to have started at the apex of the second branchial arch, about 
the base of the branchiae, which they had implicated almost to their terminal points, only leaving a 
faint fringe of what were the branchiae. The first and second arches, with their branchiae, were also 
affected. The growth did not affect the apex of the the arch externally, but passed on the internal 
surface through to both sides. The external surface of the tumor was faintly pink. On section the 
tumor was found to be homogeneous, pale in color, and soft in consistency. 
Microscopical examination. — Fibrous capsule, covered by several layers of squamous epithelium, 
from which the fine fibers forming branching and anastomosing trabeculae pass inward, inclosing more 
or less irregular alveoli. These alveoli are lined by an irregularly disposed layer of columnar cells, the 
center of each alveolus being filled with cubical cells more or less degenerated. The smaller alveoli 
are lined with columnar or cubical cells, and have the appearance of tubules cut transversely, the 
central area only containing one or two degenerated cells. Blood vessels with thin walls and wide 
lumina are found traversing the fibrous capsule and the fibrillar network within. Frequently hemor- 
rhage is met with where the slender walls of the blood vessels have ruptured. In many portions of the 
tumor the branching fibrillae with columnar cells on either side show an appearance recalling somewhat 
the fronds of the common fern. Taking into consideration the histology of the branchiae with the above 
description, it would appear that the only pathological classification, at least from the mammalian 
standpoint, which this would come under, is epithelioma (as distinguished from carcinoma). 
Gilruth gives a letter from L. F. Ayson, Chief Inspector of Fisheries, New Zealand, 
who states: 
This gill disease was first noticed there [Masterton hatchery] among the American brook trout 
(Salve linus fontinalis) in 1890, when three diseased fish were taken out that spauming season. The 
disease was peculiar to this species until the rainbow trout (Salmo irideus) were introduced, among 
which it made its appearance when they were over 3 years old. I have never found any of the 
brown trout (S.fario) affected, but took out three diseased fish from a thousand 3 and 4 year old Loch 
