684 



Cancer Research 



characin Asiyanax mcxicanus measuring 50 mm. in 

 total length and about four years old. The growths 

 occurred in the branchial region and had caused 

 exophthalmia. The tumor probably originated in a 

 paired mass of lymphoid tissue normally present in 

 the posterior region of the branchial cavity. There 

 was considerable local invasion extending even to 

 the myocardium. Metastases were present in the 

 corium of the skin, the gills, kidneys, pancreas, and 

 liver. 



AbstracU of other reported cases of Lynphosarcoma 



JoBMSTONE, 1912: The left eye of a plaice PUUichthys 

 fUsus was displaced by a retro-orbital tumor, measur- 

 ing 2 z 2 cm. The growth consisted of connective tissue 

 stroma in which were embedded masses of lymphocytes 

 separated by large spaces, apparently lymph channels. 



WiLUAMS, 1931 : A very large bulge was seen in the 

 ventral wall of a conger eel Conger conger; the over- 

 lying skin was intact. Dissection disclosed a retroperi- 

 toneal tumor, 16 X 9 cm., in the region of the kidney. 

 Within the kidney the lymphoid tissue was greatly in- 

 creased and the renal tubules were widely separated, 

 mitoses were numerous. 



Haooow and Biakk, 1933: In each kidney of a 5 

 year old American salmon Salmo solar there was a mass, 

 4.4 X 2.4 cm., that diffusely invaded these organs, re- 

 sulting in almost complete destruction of the renal 

 units. The haemal arch was occluded by a mass of 

 tumor tissue, a{^iarently by direct extension from the 

 veins of the renal portal s>'stem. 



Haooow and Blajce, 1933: Many subcutaneous tu- 

 mors were found about the bases of the fins and within 

 the buccal cavity of a partly decomposed pike Esox 

 luchts. The neoplastic tissue was gray in color and did 

 not infiltrate the surrounding musculature; vi.<<ceral me- 

 tastases were absent. Grossly the lesions appeared mu- 

 coid or fatty in character; histologically they appeared 

 to be lym{Aoid in origin. The authors suggest l>7npho- 

 sareoma as a possible diagnosis. 



Smith, Coatcs and Stkong, 1936: Neoplastic lym- 

 phoid tiMue produced a mass that was first noted in the 

 upper abdomen near the liver in a tropical aquarium 

 fifth Rasbora tateristriata. The intra-abdominal swell- 

 ing could be seen distinctly during life through the 

 semitran.<tparent abdominal wall. After approximately 

 2 months the tumor had extended cephalad, involving 

 the gin on the right side and pressing the operculum 

 outward. 



TUMORS OF PIGMENT CELLS 



Fishes are provided with an abundance of pig- 

 ment cells, not only in the epidermis and subcutane- 

 ous tiflsues, but in the peritoneum, mesentery, vis- 

 oerl, and central nervous system. The most common 

 of these ceUs in fishes as in other vertebrates are the 

 melanopbores which elaborate melanin. The guano- 

 pbores, toden with guanin crystals, and the iridio- 



cytes, bearing crystals of inorganic salts, are respon- 

 sible for the white background and the iridescence 

 so characteristic of fish coloration. In addition, 

 most fishes also possess yellow-pigmented xantho- 

 phores and red-pigmented erythrophores (allo- 

 phores). 



The close relationship of these variously pig- 

 mented cells has been generally accepted by investi- 

 gators, and their origin usually sought in a common 

 undifferentiated mesenchymal cell (8). In 1909 

 Borcca suggested that these cells may be derived 

 from the neural crest. In recent years investigators 

 working with amphibian and avian embryos have 

 accumulated convincing evidence that in these ani- 

 mals the neural crest does supply the pigment cells 

 (42). In the light of these findings it is probable 

 that the pigment cells of fishes have their origin in 

 neurectoderm. 



MELANOMA 



The most frequently observed pigment cell tu- 

 mors of fishes are the melanomas located in the skin 

 and subcutaneous tissues. They have been reported 

 in 12 species (Table 18). Whether they are pre- 

 dominantly benign or malignant cannot be clearly 

 established. Johnstone (82, 83, 85) and Prince 

 (165) reported cases in which the lesions were 

 multiple, but whether they represent metastases is 

 difficult to determine. Besides these sporadic ex- 

 amples, melanotic tumors are commonly found in 

 hybrids of the tropical aquarium fishes Xiphophorus 

 hcUerii and PlatypoccUus macuJctus. First reported 

 by Haiissler (1928) and Kosswig (1929) they have 

 been thoroughly investigated by Gordon and his co- 

 workers (59 to 63, 169). Swordtails Xiphophorus 

 hcUerii possess only micromelanophores, or no mel- 

 anopbores at all ; platyfish PlatypoccUus maculatus 

 bear both micro- and macromelanophores. It is the 

 platyfish macromelanophore factor introduced into 

 the hybrid that produces melanosis and melanotic 

 neoplasms. Although the dominant inherited factor 

 responsible for melanosis is that for macromelano- 

 phores of the platyfish, alone it is ineffectual. The 

 swordtail strain also plays its part in the production 

 of the lesion, since it contributes hereditary factors 

 that initiate the multiplication of the macromelano- 

 phores in the hybrids. 



According to the descriptions of Reed and Gor- 

 don (169) , the neoplastic disease begins as a densdy 

 pigmented spot in the caudal fin. It increases in 

 size and merges with other pigmented regions until 

 a large area is involved. Thb stage has been ob- 

 served in day-old fish as well as in embryos 6 days 

 before hatching (59). Subsequently a local swell- 



