Higher Susceptibility to N-Methyl-N'-nitro-N-nitrosoguanidine-induced Tumorigenesis in an Interstrain Hybrid of the Fish, Oryzias latipes (Medaka)

Abstract

Adult fish of an interstrain hybrid (F₁) of inbred medaka, obtained from crosses between HO4C and HB32C, were exposed for 2hr to an aqueous solution of the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine at concentrations of 15, 20, 25, 30, and 35ppm. Survival and neoplastic changes were examined over a 6-month period. A large variety of neoplasms were induced, including melanoma, papilloma, ovarian tumors, olfactory epithelioma, branchioblastoma and fibroma. More than 60% of the tumors were classified as melanoma on the basis of histological examinations. A markedly higher cumulative incidence of the melanoma with a dose-related response was demonstrated in the F₁ hybrid fish compared to the parental strains. The latent period for melanoma development, however, remained unchanged in F₁ compared to the parents. The variety of tumors induced in the F₁ fish was greater than in the parental strains. The results indicate the usefulness of F₁ hybrid fish in testing the carcinogenicity of certain water-soluble chemicals, due to their high sensitivity.