Oncozoons and the search for carcinogen-indicator fishes.

This essay attempts to bring into perspective the importance of hereditary as well as environmental factors as potential causes of neoplasms in feral fishes. Concepts delineated by Knudson regarding hereditary cancers in man and experimental animals will probably be found operative in certain demographic units (oncozoons) among feral fishes bearing neoplasms. Hereditary factors include: antioncogenes (regulatory genes), which act as suppressors of neoplastic expression in homozygous, heterozygous, or hemizygous states, as well as constitutional (structural) genes that influence carcinogen activation or deactivation through enzyme gene products, genes that influence immunologic responses, and gene abnormalities that favor spontaneous or induced mutations. The two major classes of genes (oncogenes and antioncogenes) that influence the manifestation of cancers appear to operate through different mechanisms, but conceivable interactions have not been widely investigated, especially in tumor enzootics among feral fishes. Some explorations have been undertaken in the laboratory by Anders and collaborators in studies of suppressor genes (antioncogenes) and the cellular sarc gene (an oncogene) in melanophoromas in platyfish-swordtail hybrids and backcrosses. Some feral fish oncozoons that exhibit features of hereditary oncodemes as seen in man have been tentatively identified here as candidate systems to be studied more intensively in laboratories, particularly using cytogenetic analysis and breeding methods. In the search for carcinogen-indicator fish species in feral habitats, the traditional approach has been to survey fish populations with the aim of first finding enzootics of fish neoplasia.(ABSTRACT TRUNCATED AT 250 WORDS)