Schlumberger and Lucki — Tumors in Fishes 



685 



ing develops due to proliferation of the pigmented 

 cells. The transition from melanosis to neoplasm 

 is not abrupt, and in the early stages a distinction 

 between the two cannot be made. It should be 

 pointed out here that non-neoplastic melanosis is 

 not uncommon in fishes and has recently been re- 

 ported by Smith and Coates (189) in the lung fish. 

 The neoplastic cells may be devoid of pigment, a 

 condition frequently observed in the metastases of 

 human melanomas; or they may be very heavily 

 pigmented. 



The growth of these melanomas in tissue culture 

 was studied by Grand, Gordon, and Cameron (63). 



Recently Levine and Gordon (111b) have re- 

 ported on the occurrence of pigmented ocular tu- 

 mors in xiphophorin fishes. The species distribution 

 of the neoplasms was as follows: 1 PlatypoecUus 

 maculatus, 1 Xiphophorus pygtnaeus, 6 hybrid P. 

 maculatus-X . keUerii out of a brood of 15, 2 hybrids 

 out of a brood of 16, and 1 hybrid from a private 

 collector. All fish were full grown, at least 6 months 

 old and some over a year old, before the tumor 

 developed. The average life span of the normal 

 fish is about a year and a half. Exophthalmia de- 

 veloped gradually and was associated with blindness 

 of the^afiTected eye. The neoplasms were composed 

 chiefly of pigmented epithelioid cells. They arose 

 in the choroid, invaded the retina, later they per- 

 forated the eyeball and grew into the retroorbital 

 tissues. No bacterial or virus agent could be identi- 

 fied. Although the authors stated in their paper that 

 the tumor is not controlled by a genetic factor, more 

 recent work has convinced Dr. Gordon that the tu- 

 mors develop on a genetic basis (60a). 



These tumors closely resemble the ocular neo- 

 plasms reported by Jahnel (80) and identified by 

 him as fibrosarcomas; these have been discussed in 

 the section on sarcoma. He likewise sought a genetic 

 basis for their occurrence. 



A hitherto undescribed type of pigmented tumor 

 was found in a grouper Epinephelus gigas, by DoU- 

 fus, Timon-David, and Mosinger. It is of such in- 

 terest that we shall quote an abstract made by 

 Foulds (3Sa) in full. "The primary growth was al- 

 most certainly of branchial origin. In addition to 

 tumors in the branchial region there were smallor 

 subcutaneous tumors in the caudal, anal, and dorsal 

 fins and in the liver and spleen. Some of the tumors, 

 especially in the branchial region, were plainly epi- 

 thelial, resembling basal cell tunrars of mammals. 

 Some of the cells were pigmented and, since pigmen- 

 tation seemed associated with an eusin^ihilic de- 

 generation, it appeared as if the melanin granules 

 represented a degenerative phenomenon. In the liver 

 and spleen, however, though almost all the tumor 

 cells were pigmented there was do sign of a degenera- 

 tive process; careful examination revealed rare tu- 

 mor nodules with celb like those in the branchial 

 tumors. None of the tumor cells resembled the 

 melanocytes characteristic of lower vertebrates. 

 Transitions were found between epithelial cells de> 

 void of pigment and melanotic cells in which the 

 abundance of pigment was explicable only by an 

 active production of melanin. The most likely hy- 

 pothesis is that the tumor cells of epithelial origin 

 acquired secondarily the {xiwer of forming melanin. 

 Previously described melanomas in fishes were pre- 

 dominantly sarcomatous in ap p earan ce . It b sug- 



