Return to the Table
of Contents
Next Section of
the Tumor Manual
Previous Section
of the Tumor Manual
4. NEOPLASMS OF WHITE SUCKERS (Catostomus commersoni) AND REDHORSE SUCKERS (Moxostoma sp.)
4.1 Neoplasms of the skin and mouth
These neoplasms appear as 2-20 mm, non-pigmented, nodular or cauliflower-like growths on the lips and body (including the fins) of white suckers (Figure 6). They may occur singly or in clusters on the lips but tend to occur singly on the body and fins. Histologically similar growths have also been reported on redhorse suckers (black 1983). The lesions are easy to recognize and having once seen a few examples, there are few conditions which could be mistaken for this disease in white suckers. Invasive lip tumors are rare but have been confirmed in white suckers (Smith et al. 1989). Similarly, papilloma-like neoplasms on the body have been diagnosed as squamous cell carcinoma, dermal sarcoma, dermal fibrosarcoma and fibroma. These lesions are rarely found on immature suckers but may increase rapidly following sexual maturity (Sonstegard 1977). Prevalence rates for lip papillomas exceed 50 percent in fish greater than 10 years old at some locations on the Great Lakes (Hayes et al. 1990). Background prevalence appears to range from 0 to 15 percent (Government of Canada 1991). The occurrence of body papillomas on Lake Ontario suckers ranges from 1 to 10 percent. Most of the available tumor prevalence data in the Great Lakes was collected from white suckers during their spring spawning migrations.
Etiology
Lip papillomas in white suckers may proliferate or regress spontaneously. Recent studies have confirmed that lip papillomas proliferated when the fish were held under crowded conditions and disappeared when crowding was relieved. These observations suggest a non-chemical etiology for white sucker lip papillomas. The occurrence of lip papillomas varies in Lake Ontario from 6 percent to 62 percent. Increased prevalence occurs in the more urban/industrialized western part of Lake Ontario.
4.2 Neoplasms of the liver
Although liver neoplasia may be less common in white suckers than in some other species such as the brown bullhead, both hepatocellular tumors (neoplasms originating from hepatocytes) and cholangiolar tumors (neoplasms originating from the bile ducts) have been found in Lake Ontario fish (Figure 7) (Hayes et al. 1990). The gross appearance of these neoplasms is similar to liver tumors found in the brown bullhead. The white sucker liver is attached by mesentery to the stomach and intestine and is much longer and thinner than the bullhead liver. As a result, large embedded tumors are detectable without slicing the liver, and the increased surface area makes it easier to detect small neoplasms. Most hepatocellular and cholangiolar neoplasms occur on the posterior, ventral lobes of the liver in white suckers, but cholangiomas have been found on the anterior dorsal lobe and on the dorsal surface adjacent to the gall bladder.
Confounding lesions
Chronic inflammatory liver diseases caused by parasitic trematodes and nematodes can cause local liver necrosis, inflammation, and extensive proliferation of the bile ducts (Hayes et al. 1990). The disease produces large white or cream-colored nodules that appear grossly like a cholangiolar carcinoma. In addition, parasitic cysts are frequently found in the liver and throughout the viscera of wild fish. They appear grossly as nodules that can easily be "shelled out" (discrete masses that can be removed from the surrounding tissue without tearing). Other confounding lesions include granulomatous diseases (Figure 8).
Etiology
Liver tumors in white suckers are suspected to have a multifactorial etiology involving liver disease and chemical carcinogens (Kirby et al. 1995). Parasites migrating through the liver cause a proliferation of the hepatocytes and bile cells. In the presence of chemical carcinogens, cellular proliferation may result in cell replication before repair mechanisms have removed any chemical-DNA adducts (MacCubbin et al. 1990).
Parasitic disease occurs in low levels throughout the Great Lakes but is most severe in urban areas in the lower Great Lakes. A tumor survey of white suckers from Lake Ontario and a reference site on Manitoulin Island, Lake Huron found that severe liver disease occurred in fish from Lake Ontario along with concurrent hepatocellular and biliary neoplasms (Government of Canada 1991). White suckers from the reference site had mild liver disease and no neoplasia.
4.3 Neoplasms of the digestive tract
Few digestive tract cancers have been observed to date, and only in redhorse suckers (Black 1983). Unfortunately, no illustrations of the gross appearance are available. Typical digestive tract neoplasms are plaque-like raised growths or cauliflower-like masses appearing to originate from the lining of the stomach or intestines. A distended lower intestine may be symptomatic of these neoplasms.
Confounding lesions
Intestinal parasites and granulomas may be confused with neoplasms.
Etiology
No causative agent has been identified. However, chemical analysis of gut contents indicates that white suckers from polluted environments are exposed to a variety of contaminants including carcinogens from their food and from ingested sediment. Dietary exposure is suspected to play an important role in the etiology of liver tumors and may be implicated in digestive tract neoplasms.
5. NEOPLASMS OF FRESHWATER DRUM (Aplodinotus grunniens)
5.1 Neoplasms of the skin
These lesions are common in freshwater drum from eastern and central Lake Erie, the upper Niagara River, and western Lake Ontario, and may occur elsewhere throughout the lakes (Black 1983). They appear to originate from cells oppositional to the base of the scales (Black 1983). Early stages of development are similar in color to the surrounding area and are difficult to detect. Dermal neoplasms may occur anywhere on the fish including the head, trunk, or fins. The prevalence of the disease in relation to species distribution, either within or outside of the Great Lakes, has not been well documented.
The diagnosis of these neoplasms is uncertain at present (Figure 9). Examples of the same lesion have been diagnosed as fibromas, neurolemomas, pigmented neurolemomas, and chromatoblastomas/chromatophoromas (multipotential pigment cell tumors). Histologically similar neoplasms occurring in a marine species of croaker, the nibe (Nibea mitsukurii), have been diagnosed as chromatophoromas/blastomas (Kinae et al. 1990). It is interesting that neoplasms in different anatomic locations in the nibe, produce different cell products. Neoplasms occurring on the dorsal aspect of the fish produce guanine (the material which give fish their iridescent quality). The dermal neoplasms of freshwater drum appear to be similar to neoplasms described in the nibe and may also be pigment cell neoplasms, although substantial amounts of collagen fibers are present, especially in the neoplasms which have developed on the dorsal surface of the fish (Black 1983).
Confounding lesions
It is conceivable that excessive wound repair or bacterial and fungal infections could be mistaken for dermal neoplasms. However, these neoplasms are easy to recognize and after viewing several examples, the observer should easily be able to recognize the dermal growths.
Etiology
No agent(s) or factors causing any neoplasms in freshwater drum have been identified. The geographic distribution of dermal neoplasms in freshwater drum suggests they may be a suitable tumor monitoring species, but the evidence supporting a chemical etiology is weak (Black 1983). The tumors can sometimes be dislodged through contact and prevalence data may be influenced by sampling methods.
5.2 Neoplasms of the liver
A few liver neoplasms (well differentiated hepatocellular carcinomas) have been observed in this species. All were collected from Eastern Lake Erie (Black 1983).
Confounding lesions
With respect to liver tumors, the confusion potential of granulomatous diseases and parasites apply. Freshwater drum from eastern Lake Erie, also have a high prevalence of a type of proliferative kidney disease which grossly and sometimes microscopically appears neoplastic; however, a protozoan parasite is present in the lesions and is the suspected causative agent.
6. NEOPLASMS OF YELLOW PERCH (Perca flavescens)
6.1 Neoplasms of the gonad
Gonadal tumors are thought to originate from the smooth muscle components of the testis and have been observed in populations of male yellow perch from various locations in the Great Lakes (Budd et al. 1975). Gonadal tumors are less common in females. Grossly, gonadal tumors are variably sized (2-20 mm), smooth surfaced, white or cream-colored masses which appear as an outgrowth from the testis (Figure 10). They may occur as single or multiple growths and may occur bilaterally. They may be difficult to detect in situ but are easily seen if the gonads are removed.
Confounding lesions
Protozoan parasitic cysts occur as variably sized, smooth surfaced, white, acellular, and avascular-looking nodules. These cysts are potential confounding lesions for all neoplasms, but especially in the testis. We have not observed any of these cysts in yellow perch testis.
Etiology
No agent(s) or factors have been identified. The tumors have been found in perch from non-polluted areas such as South Bay on Manitoulin Island, Lake Huron (prevalence of 5 percent) and Georgian Bay and in lakes within Algonquin Park in Ontario (Budd et al. 1975). A chemical etiology is not suspected. Interestingly there is no record of this neoplasm in yellow perch from Lake Erie.
7. NEOPLASMS OF SAUGER (Stizostedion canadense) AND WALLEYE (Stizostedion vitreum)
7.1 Neoplasms of the skin
Histologically similar dermal growths have been observed in both walleye and sauger (Black et al. 1982). They can occur singly, or as multiple coalescing groups of variably sized, fleshy nodules anywhere on the fish's body (Figure 11). These white or pale yellow/pink, smooth neoplasms are firm to the touch and may produce a slightly gritty sensation when cut with a knife. Histologically, these lesions have been diagnosed as benign dermal fibromas or as invasive fibrosarcomas with and without foci of ossification (bone formation). Where bone formation is present the diagnostic terminology is modified eg. ossifying dermal fibroma.
Confounding lesions
Dermal fibromas and fibrosarcomas are often confused with lymphocystis, a viral disease in which epidermal cells infected with virus become massively enlarged (Bowser et al. 1988). This leads to the formation of plaque-like, nodular or cauliflower-like masses that may be white, gray or cream-colored and somewhat translucent (Figure 12). The lymphocystis lesion is softer and usually cuts with less resistance. Inspection of the cut surface of a lymphocystis lesion with a 10X hand lens will reveal the enlarged cell structures. Based upon gross appearance alone, it is doubtful whether dermal lesions could be correctly diagnosed.
Etiology
Virus are associated with the lesion and a viral etiology is suspected (Yamamoto et al. 1985).
7.2 Neoplasms of the liver
Epizootic liver neoplasia has been observed in sauger, and to a lesser extent, walleye, from Torch Lake and the Keweenaw Waterway, Michigan (Black et al. 1982). Liver tumors have also been reported in walleye from the St. Lawrence River and the Bay of Quinte (Hayes and Portt unpubl.). In Torch Lake, hepatocellular neoplasms affect nearly 100% of the sauger and about 5-10% of the walleye (Black et al. 1982). Grossly, small neoplasms appear as pale, almost translucent, 2-3 mm foci, located just beneath the liver capsule. Advanced neoplasms may range in size from 10 to 20 mm in diameter and appear as gray, yellowish, or reddish-tan (liver colored) nodules which may bulge outward from the liver surface 10 mm or more (Figure 13). Very rarely a tumor is observed that is attached to the liver only by a very thin strand of liver tissue (peduncle).
Confounding lesions
Liver lesions in most species of fish appear grossly similar and all can be confused with parasitic cysts and granulomatous disease.
Etiology
Torch Lake, and to a lesser extent the Keweenaw Waterway, have received large amounts of copper mining wastes, including organic chemicals, used by the mining industry (Black et al. 1982). The absence of reports of liver tumors in sauger from other sites in the Great Lakes, combined with the known history of chemical exposure, suggests a chemical etiology. Torch Lake sauger are more heavily parasitized than the walleye and chronic injury resulting from parasitism may result in tumor promotion (Black et al. 1982).
8. NEOPLASMS OF CARP X GOLDFISH HYBRIDS (Cyprinus carpio X Carassius auratus)
8.1 Neoplasms of the gonad
Carp x goldfish hybrids from the Great Lakes exhibit high frequencies of benign gonadal tumors (almost 100 percent of older male hybrids have tumors) (Sonstegard 1977). The tumors are most common in males but are also found in females. Grossly, the tumors appear as smooth or cauliflower-like nodules ranging from 1-10 cm in diameter (Figure 14). However, oblong masses 3-4 cm long are more common. Testicular tumors are white to cream-colored and may occur on one or both gonads. All tumored hybrids are sterile (Sonstegard 1977). Hermaphrodism is common and tumored fish frequently have both testicular and ovarian tissues. In the female, the tumors are frequently characterized by large, fluid-filled sacs and the presence of testicular tissue. Advanced tumors are often detectable by the presence of a grossly distended abdomen, however, most will be detected only by internal examination. Gonadal tumors are rarely found on immature fish and prevalence increases with age (Down et al. 1988). The condition also occurs on carp and goldfish but at low frequencies (Sonstegard 1977).
Confounding lesions
Possible confounding lesions include the gonadal response to parasites and the occurrence of granulomas. The gonads of hermaphroditic fish are understandably confusing and may be mistaken for a neoplastic condition.
Etiology
Museum specimens of carp X goldfish hybrids collected prior to 1952 from Lake Michigan and Lake Erie exhibited low tumor frequencies (Sonstegard 1976 in Sonstegard 1977). Hybrids collected from the same areas in the 1970s exhibited high frequencies of gonadal tumors. Recent collections from at least seven sites on the Great Lakes, including a relatively uncontaminated bay on Lake Huron, indicated that at least 50 percent of the adult male hybrids have gonadal tumors (Sonstegard 1977). The occurrence of tumored hybrids from relatively clean sites and the possibility of genetic dysfunction resulting from hybridization suggest a non-chemical etiology (Sonstegard 1977). It should be noted that the hybrids probably have abnormal pituitary-gonadal feedback regulation which make them susceptible to excessive production of gonadotrophic hormones, which in turn leads to stimulation of the gonadal tissues and possibly to the formation of tumors.
9. NEOPLASMS OF NORTHERN PIKE (Esox lucius) AND MUSKELLUNGE (Esox masquinongy)
9.1 Neoplasms of the skin
Lymphosarcoma is a common disease involving the skin and dermis of northern pike. It occurs throughout North America and Europe and may reach prevalence rates of 10-20 percent (Sonstegard 1976). The disease in muskellunge has been observed from Lake Huron and the St. Lawrence River. The symptoms of the disease are similar in both the northern pike and muskellunge. Anatomically, the lesions can occur anywhere on the body. Grossly, the lesions vary in appearance depending upon their anatomic location. For example, skin lesions usually occur as reddish-purple "blisters" and ulceration is common (Figure 15), whereas fin lesions (the pelvic fin is commonly affected) appear as a greatly thickened irregular mass enveloping the fin. Jaw lesions produce reddening and thickening of the gingival tissue and lesions of the head may be a single nodule or appear as multiple coalescing groups. The occurrence of lymphosarcoma is cyclic and prevalence is highest in the spring and fall. It is almost always fatal to muskellunge (Sonstegard 1976).
Confounding lesions
Most lesions characterized by open sores (ulcers) can be confuse with lymphosarcoma. Similar symptoms may result from wounds, parasites (including lamprey), and bacterial, fungal, and viral infections. The need to confirm field diagnosis with histological diagnosis cannot be over emphasized.
Etiology
Extensive data indicate an infectious etiology. Lymphosarcoma is transmissible by inoculation of cell-free homogenates in northern pike, and in both species, cell-free homogenates yield evidence of the presence of an RNA virus (Papas et al. 1976). These diseases appear to have a viral etiology (Sonstegard 1976). Because of the pronounced seasonal variation in disease prevalence, samples collected at different seasons and/or water temperatures, will yield different prevalence data and confound temporal and spatial analysis.
10.1 Thyroid Hyperplasia in coho salmon (Oncorhynchus kisutch) and pink salmon (Oncorhynchus gorbuscha)
Thyroid hyperplasia is characterized by single or multiple off-white or pink nodular growths (3-15 mm), bulging from the base of the gill arches (Figure 16). Although coho salmon are most frequently affected, hyperplasia has been reported in chinook salmon, pink salmon and rainbow trout. The condition is found throughout the Great Lakes. Data collected in 1976 and 1980 reported prevalence rates of 6.3, 47.6 and 79.5 percent in coho salmon from Lakes Michigan, Ontario, and Erie respectively (Moccia et al. 1977). More recent data suggest that prevalence has declined substantially in Lake Ontario. Thyroid hyperplasia is uncommon in immature fish and develops rapidly several weeks before spawning. There are no known adverse effects of thyroid hyperplasia on the adult fish although the occurrence of large thyroid hyperplasia lesions and reproductive dysfunction has been reported in salmon from Lake Erie (Noltie et al. 1988).
Thyroid hyperplasia is not considered a neoplastic disease. However, a percentage of these lesions exhibit significant invasion of muscle, cartilage, bone, and even blood vessels. Invasion of blood vessels is usually considered a diagnostic feature of cancer (Black 1984). Although no one has demonstrated regression of the disease in feral coho salmon in response to iodine administration, classical studies of thyroid hyperplasia in brook trout indicated rapid regression of the goiters when iodine was added to the diet or the water (Black 1984).
Etiology
Goiter was endemic in the human population in the Great Lakes area prior to the use of iodized salt, suggesting that the low iodine content of the lakes, especially in a marine adapted fish, may be an underlying factor. However, the absence of a correlation between lake iodine levels and the prevalence of thyroid hyperplasia and the presence of goiter in Great Lakes herring gulls suggests the possibility of a goiterogenic agent.
10.2 Thymic lymphoma/lymphosarcoma of splake (Salvelinus namaycush X Salvelinus fontinalis)
This neoplasm has been reported in hatchery fish. There are no reports of thymic lymphosarcoma in Great Lakes fish. It appears as single or multiple nodules (3-10 mm) located on the dorsal aspect of the opercular cleft.
Etiology
The causal agents have not been confirmed but there is strong evidence that this tumor is associated with a virus. The presence of the condition in hatchery fish suggests that chemical contaminants are not implicated in the etiology.
10.3 Neural tumors
A limited epizootic of neoplasms originating from neural tissue (neuroblastoma) have been observed among coho salmon reared in chlorinated, then dechlorinated, non-process cooling water in the state of Oregon (Meyers and Hendricks 1984). To date, a single neurofibroma tumor has been observed in a chinook salmon from Lake Michigan. Grossly, the tumors appear as large bulging masses that displace muscle and epidermis. A single example of an olfactory neuroepithelioma in a Lake Michigan whitefish (Coregonus hoyi) is recorded at the Registry for Tumors in Lower Animals (RTLA), (accession no. 257) (Harshbarger 1965-1988). No examples of intracranial neoplasia are presently known from fish, but this simply may reflect the difficulty of detecting these neoplasms.
10.4 Neoplasms originating from fibroblasts or fibroblast-like cells
Neoplasms composed of bundles of uniform spindle shaped cells are usually diagnosed as fibromas. More invasive neoplasms originating from the same cell type are diagnosed as fibrosarcomas. Fibromas and fibrosarcomas may occur externally or internally.
Fibromas are among the more common neoplasms occurring in feral fish and were described for freshwater drum. In the Great Lakes, fibrosarcomas have been found occasionally in the peritoneal cavity of goldfish (Carassius auratus), and on the occipital area of a Lake Erie coho salmon. Fibrosarcomas have also been diagnosed in walleye from Lake St. Clair, yellow perch from Lake Huron, and white suckers from Lake Ontario. There are no characteristic features that distinguish dermal fibromas and fibrosarcomas from epidermal papillomas, squamous cell carcinomas, or lymphocystis.
10.5 Kidney tumors
Reports of renal tumors in Great Lakes fish are rare. A single kidney
tumor in smelt is recorded at the RTLA (accession no. 2810) (Harshbarger
1965-1988). Similar tumors have been induced in rainbow trout following
experimental laboratory exposures to direct acting carcinogens. Nodular
kidney masses should be regarded as suspicious. The presence of kidney
neoplasms are confounded by parasites, granulomas, and several non-neoplastic
proliferative kidney lesions such as polycystic kidney disease.
Return to the Table
of Contents
Next Section of
the Tumor Manual
Previous Section
of the Tumor Manual