Carcinogenicity tests with rainbow trout embryos: a review

Abstract

Methods of exposure and results of laboratory carcinogenicity tests using rainbow trout are reviewed. Although the rainbow trout has had significant use as a model of aflatoxin-induced liver cancer, the species has not yet been widely used as a bioassay species for carcinogen testing. The observation that rainbow trout embryos were susceptible to carcinogen exposure by immersion in aqueous solutions of test agents was discovered in research with aflatoxin. The aqueous exposure method had numerous advantages, but did not work well with some chemicals. Subsequently, closed system methods of micro-injection into the perivitelline space and the yolk-sac have also been developed which can be used to obviate the limited permeability of the chorion to some chemicals. An additional method of exposure involves topical application of a dimethylsulfoxide containing carcinogen solution onto the egg surface. Results to date suggest that carcinogen tests using rainbow trout embryos will detect most direct-acting alkylating agents such as dimethylnitrosamine, N-methyl-N′-nitro-N-nitrosoguanidine, methylnitrosourea, etc. and some agents requiring metabolic activation, such as aflatoxin B 1 and benzo( a)pyrene, but the range of the rainbow trout embryo assay to a broad range of chemicals has not been fully studied. Limited data from one laboratory suggest that rainbow trout may lack the ability to activate aromatic amines such as 2-acetamidofluorine, 2-naphthylamine, and 4-aminobiphenyl to carcinogenic metabolites. Methods of exposure useful for carcinogenicity testing may also be applicable to teratology and ecotoxicology.