Establishment of a Cell Line from the Platyfish-Swordtail Hybrid Melanoma¹

A fish melanoma cell line, PSM-1, was established from a hereditary melanoma in an interspecific hybrid of Xiphophorus for cytogenetic studies of this melanoma system. An amelanotic melanoma was obtained from the tail fin of a melanotic F₁ hybrid between a spotted platyfish (Xiphophorus maculatus) and an albino swordtail (Xiphophorus helleri). The tumor tissue was dissociated and cultured in Eagle's minimal essential medium supplemented with 10% fetal calf serum. PSM-1 has been maintained for 52 passages and 29 months in vitro since March 3, 1978. This cell line showed considerable variation in cellular morphology. Although no apparent pigment was detectable by light microscopy, melanosomes and premelanosomes could be seen under the electron microscope. The cells grew randomly across each other with an apparent lack of contact inhibition and formed many clumps. The doubling time was approximately 2 days, and the modal chromosome number at the 41st passage was a near triploid 71. A high tyrosinase activity was detected. PSM-1 is similar to some mammalian melanoma cell lines with respect to cytological characteristics and growth patterns.