[Quantitative analysis of melanoma growth in tumorous fish of the genus Xiphophorus after partial-body X-irradiation with therapeutic doses (author's transl)].

Hereditary melanomas in Xiphophorus helleri, caused by the spotted dorsal gene, Sd, and its modifiers, have arisen by introgressive hybridization of X. maculatus X X. helleri-hybrids with X. helleri. 7 of those melanotic poeciliid fish had been X-irradiated, 10 tumorous sibs from the same brood were kept as controls. The total X-ray dose of 9000 R was fractionated into partial doses of 5000 R and 4000 R, respectively. Only the melanomatous regions of the caudal peduncle and those of the dorsal part of the body, the dorsal and caudal fins included, were irradiated. The rest of the trunk was shielded with lead against radiation. The teleosteans were 162 days old when irradiated for the first time; the second exposure followed 193 days later. In intervals of 14 or 21 days, the animals had been photographed, and the melanotic areas of the enlarged prints had been determined by planimetrical measuring. After this, they were calculated as percent of the total body surface, both with and without the dorsal fin area. There was a significant regression of melanoma growth in irradiated fish.