Neoplasms in Rainbow Trout, a Sensitive Animal Model for Environmental Carcinogenesis*

Vacuolation, proliferation and neoplasia in the liver of Boston Harbor winter flounder (Pseudopleuronectes americanus)

“…These species include the danio (Stanton 1965), rainbow trout (Halver 1967, Sinnhuber et al 1976, Hendrcks et aL. 1980, 1981& 190 1985, the meda (Ishikawa et al 1975, and, Poecilopsis (Schultz and Schultz 1984) and the guppy (Hawkins et al 1990).…”

Initiation, Promotion, and Inhibition of Carcinogenesis in Rainbow Trout

“…Early studies of the zebra danio (Brachydanio rer?io) and the guppy (Lebistes reticulatus) (10)(11)(12)(13)(14)(15)(16)(17), and later experiments with the Japanese medaka (Oryzias latipes), the species Poeciliopsis, and other aquarium fish (18)(19)(20)(21)(22)(23), have revealed liver to be a major target organ and hepatocellular carcinoma to be the most prevalent tumor type in fish carcinogenic response. Hepatocellular carcinoma is also the most common neoplastic response in trout (9,(24)(25)(26)(27)(28), though other neoplasms, including nephroblastoma, gastric and swim bladder papillary adenoma, and fibrosarcoma can be induced, depending on carcinogen used, exposure route, and dose. For example, dietary exposure to Nmethyl-N'-nitro-N-nitrosoguanidine (MNNG) induces only gastric papillary adenomas in rainbow trout, whereas embryonic or fry water exposure to a solution of MNNG also induces hepatocellular carcinoma, nephroblastoma, and swim bladder papillary adenoma (8).…”

Suspected toxicopathic hepatic necrosis and megalocystosis in pen-reared Atlantic salmon Salmo salar in Puget Sound, Washington, USA

“…Megalocytosis and nuclear pleomorphism are interpreted as chronic manifestations of hepatocarcinogen toxicity, resulting in aneuploid hepatocytes as a consequence of disrupted mitosis (Wales 1967, Sinnhuber et al 1977. Although hepatocytes with extremely enlarged nuclei are likely terminally degenerate cells, they may indicate that the liver has been exposed to a toxicant-carcinogen and could ultimately develop hepatic neoplasms if the fish were to survive.…”

“…Diffuse necrosis with concurrent regenerative islands and hepatocellular pleomorphism, referred to as megalocytosis when nuclei are tremendously enlarged (Wales 1967), are consistent features in the liver of rainbow trout Salmo galrdneri fed diets containing the potent hepatocarcinogen aflatoxin. Affected trout surviving the initial toxic effects of this carcinogen exhibit a high incidence of liver neoplasia (Ashley 1967, Simon et al 1967, Sinnhuber et al 1977'aIes 1357, Ws!es e! e!.…”