370 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 1 902 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 on 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 trabeculse 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 

 (Salvelinus foniinalis) in 1890, when three diseased fish were taken out that spawning 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 



