1915. | T. SOUTHWELL : Indian Parasites of Fish. S77 
(6) Carcinoma of the Thyroid in rainbow trout (Salmo 
irideus) from Naini Tal. 
(Plate xxvi, figs. I and 2). 
During the early part of 1914, the Dy. Conservator of Forests, 
Naini Tal, United Provinces, India, in a letter to me, stated that 
numbers of rainbow trout (Salmo irideus) were dying in the hill- 
waters in the vicinity of Naini Tal. I requested him to forward 
to me specimens of the dead fish, preserved in spirit. In all, I 
received 13 specimens. The largest measured 154 inches and the 
smallest ro inches. ‘There were 4 or 5 females with ripe eggs. No 
external or internal parasites were discovered. Three of the fish 
had a small abrasion on the body. These wounds, however, were 
occasioned during packing and transit, and were in no way con- 
nected with the death of the fish. Out of the 13 fish sent, tumours 
were found on the gills of three. Excepting the tumours just 
mentioned, the fish appeared normal and well fed. The location 
of the tumours was as follows :-— 
(1) A small trout 10 inches long.—The tumour was situated in 
the gills, on the convex (postero- ventral} edge of the gill-arches on 
the right side. Only one tumour was present (plate xxvi, fig. 2). 
It measured 17 mm. long, g mm high and 4 mm. thick. The 
outer surface of the gills in the vicinity of the tumour was slightly 
pigmented with biack. The tumour did not involve the bony 
branchial arches, but only the gill-filaments in the vicinity, 7... 
the tumour replaced the gill-filaments. The gill on the last bran- 
chial arch was the only one not involved. 
(2) A large trout 154 inches.—Two tumouts, one in each bran- 
chial cavity, visible ventrally as coarsely nodulated or lobated 
masses in the anterior extremity of each branchial chamber. ‘The 
one on the right side was larger than that on the left. The mea- 
surements were as follows :— 
Large tumour—long 20 mm., high 13 mm., thick Ir mm. 
Small tumour— ,, 14 ,, * Geet eee say 
The external gill-filaments on the right side were only slightly 
affected. The cotresponding gill-filament on the left side was not 
involved. 
(3) A medium-sized fish Two tumours situated as in (2), 
both of the same size and measuring 20 min. long, 14 mm. high 
and 15 mm. thick. 
The latter tumours were situated at the anterior extremity of 
the branchial chamber just below the eye, and were sufficiently 
bulky to project into the buccal cavity. The tumours consisted for 
the most part of a yellow-white cheesy substance enclosed in a thin, 
but slightly tough, fibrous capsule. The tumours were not pedun- 
culated, but were supported by the capsule, which was attached 
at various places to the anterior wall of the branchial chamber. 
Posteriorly the cyst was free. Anteriorly the two tumours were in 
contact in the centre line. The tumours consisted entirely of the 
caseous substance referred to above. 
