The viviparous fish Poecilliopsis from northwestern Mexico is characterized according to its potential in cancer research. A colony of these fishes started in 1961 includes inbred strains of P. lucida (M61-9, M61-31, M61-35, and S68-4), P. monacha (S68-4 and S68-5), and P. viriosa (M65-23), which have been demonstrated by electrophoresis and tissue graft analysis to be homozygous. All-female species of hybrid origin are represented by 12 clones which, although highly heterozygous, are genetically identical isogenic and readily accept within-clone tissue transplants. Two studies are cited in which hepatic tumors were chemically induced. Hepatic tumors, initially induced with DENA have been successfully transplanted into the muscle tissue and abdominal cavity of members of the same strain.