PARASITES AND TUMORS IN FISH
Parasites
Anglers sometimes catch fish which contain worms, grubs, cysts, or nodules in the flesh. When cleaning fish, anglers may notice worms in or around the intestines of the fish, or fungus growths on the skin, fins, or gills. These parasites of fish are a normal part of the ecosystem in which the fish lives. While not esthetically pleasing, the edible portions containing parasites, if properly and thoroughly cooked, do not present a health hazard.
Some of the most commonly seen parasites of fish are black spots, yellow grubs, and tapeworms. Most fish have parasites, and they seldom affect the well being of the fish except under unusual conditions. Parasites in fish are only a problem when fish are not thoroughly cooked or are eaten raw.
Black Spot
Black spot is caused by a parasite called a fluke, which burrows into the skin of fish. The black pigment (about pinhead size) forms in the tissue surrounding
the fluke and is a reaction of the fish caused by the parasite. The fluke itself is actually a whitish color.
Yellow Grub
Yellow grubs are also caused by a fluke, which penetrates the skin of fish and curls up into a sac under the skin or in the muscle where it grows to be the grub. The grubs are often found in the flesh of fish near the dorsal fins. When freed from the sac, the grub may be up to
2-inch long.Tapeworms
Young tapeworms are common in the organs and body cavity of many fish. They usually live in the internal organs of the fish. They resemble long, thin ribbons about
1/16-inch wide.Tumors
Occasionally, anglers catch fish with external growths, tumors, sores, or other lesions. Such abnormalities generally result from viral or bacterial infections. Abnormalities in the liver or intestines are sometimes seen in tolerant fish such as White Suckers and Brown Bullheads, and can be caused by parasites or tumors. Concern about the potential effects of these diseases on the fish themselves, and the possible role of pollution in causing tumors in some coarse fish, has prompted ongoing investigations into these abnormalities. Growths on game fish caused by viruses include lymphocystis, dermal sarcoma, and lymphosarcoma.
Viruses infect fish skin through contact with infected fish during the spring spawning run, forming pale or white cauliflower-like growths. Lymphocystis does not kill affected fish, and tagging studies have shown that these fish can lose the growths by the following spring. There is no known health risk from consuming an infected fish once it has been skinned and cooked.
Dermal sarcoma, another viral disease affecting walleye, is caused by viruses which infect cells and cause growths just under the skin. These growths can be removed by skinning the fish.
The appearance of viral or bacterial infections in fish may be unsightly, but there is no evidence to suggest that these infections pose a threat to consumers of infected fish.
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