Fish oncology is important not only because of the effects of neoplasms on individual fish and fish populations, but also because fish are good models for furthering our understanding of neoplasia in general. Fish are especially useful in the evaluation of carcinogenicity of chemicals (Hoover, 1984a; Metcalfe, 1989; A. Anders et al., 1991b; Hawkins et al., 1995; Bailey et al., 1996), the study of mechanisms related to carcinogenicity (Bailey et al., 1989), and the determination of genetic factors that regulate oncogenesis (F. Anders et al., 1984; F. Anders, 1991). Fish neoplasms can also serve as indicators for the presence of environmental carcinogens (Dawe and Harshbarger, 1975; Sonstegard and Leatherland, 1980; Couch, 1982; Grizzle, 1985, 1990; Dawe, 1990).

In this chapter, we review the neoplastic diseases of fish with an emphasis on aetiology. Selected non-neoplastic lesions that could be confused with neoplasia are included, and differences and similarities between these lesions are discussed. Laboratory experiments have demonstrated that certain viruses, chemicals, inherited characteristics and radiation can cause neoplasms in fish. Although causes of neoplasms in wild fish are more difficult to ascertain, there is strong evidence that chemical pollutants and oncogenic viruses are important in certain fish populations. In other instances, neoplasms occur sporadically and at very low prevalency so that epizootiology may not be useful for determining the nature of the aetiological agent.

Most general reviews of fish neoplasms have been organized phylo-

genetically or by tissue, organ, or organ system (Schlumberger and Lucke, 1948;

Nigrelli, 1954; Wellings, 1969; Mawdesley-Thomas, 1975; Peters, 1984; Hayes and Ferguson, 1989; Roberts, 1989; Sindermann, 1990). These references can be consulted for an overview of the types of neoplasms that occur in fish. Fish have been included in discussions of comparative oncology (Squire et al., 1978;

Dawe, 1982), and several symposia have provided overviews of fish oncology

© CAB INTERNATIONAL 1998. Fish Diseases and Disorders, Volume 2: Non-infectious Disorders (eds J.F. Leatherland and P.T.K. Woo) 37

(Dawe and Harshbarger, 1969; Dawe et al., 1976; Kraybill et al., 1977; Dawe et al., 1981; Hoover, 1984a; Malins, 1988). Previous reviews of aetiological factors associated with fish neoplasia have focused on viruses (Gross, 1983), pollutants (Couch and Harshbarger, 1985; Mix, 1986; Malins et al., 1988; Grizzle, 1990; Harshbarger and Clark, 1990; Black and Baumann, 1991; GESAMP, 1991; Bucke, 1993; Harshbarger et al., 1993) or chemical carcinogens generally (Moore and Myers, 1994; Hawkins et al., 1995; Bunton, 1996).

The Registry of Tumors in Lower Animals is an important resource fostering study of neoplasms of fish and other poikilothermic animals (Harshbarger, 1977; Harshbarger et al., 1981). The Registry was previously housed in the Smithsonian Institution and is now located in the Department of Pathology, George Washington University Medical Center, Washington, DC. Funded by the US National Cancer Institute, the Registry has maintained a collection of specimens and literature related to neoplasms and related disorders of invertebrates and poikilothermic vertebrates. Specimens originate from natural habitats, zoos, aquaria and laboratory experiments. Under the direction of Dr John C. Harshbarger, the Registry has developed a worldwide reputation as a source of specimens for study and of information about neoplasms of lower animals.

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