Usefulness of the guppy, Poecilia reticulata, in carcinogenicity testing: special advantages and problems.

The guppy, Poecilia reticulata, native to fresh and brackish waters of northeastern South America and adjacent islands of the Caribbean, has been introduced throughout much of the tropical and subtropical world. It tolerates comparatively wide ranges of temperature, salinity, and crowding. This hardiness plus high fecundity, live birth, fast growth, and early maturation make it an excellent laboratory organism for disciplines ranging from behavioral studies to toxicity testing. In 4 published carcinogenicity studies, 8 of 11 known mammalian carcinogens produced neoplasms in the liver and occasionally at other sites. The guppy's overall popularity, however, has magnified problems concerning stock origin. The natural variability of this species has been increased by artificially selected breeding and by exotic natural selection pressures of foreign environments on introduced populations. The source of many guppy stocks today is ultimately the pet trade, and a good genetic history of such strains is not often available. Differences in stock origin may account for some differential responses of growth and sensitivity to environmental variables noted in the literature. The establishment of carefully maintained inbred strains for cancer research is the best solution to this problem.