Becker, George C. / Fishes of Wisconsin
Fish parasites, pp. 38-42 PDF (1.7 MB)
Fish Parasites Like other vertebrate animals, fishes have parasites. I have generally refrained from listing these in the species accounts; the material in this section is pro- vided for the fisherman who is curious about parasites in fish he has just caught. I have simplified this section by listing only the most frequently encountered parasites. Further details dealing specifically with the parasites of Wisconsin fishes can be found in Marshall and Gilbert (1905), Pearse (1924a, 1924b), Cross (1938), Bangham (1944), Fischthal (1945, 1950, 1952, 1961), Degurse (1961), An- thony (1963), and Les (1975). Useful general works on the parasites of North American fishes are Davis (1956) and Hoffman (1970). The YELLOW GRUB (Clinostomum marginatum) appears as a small (about 6 mm long) whitish or yellowish cyst deep in the flesh of the fish, or occasionally just beneath the skin. Yellow perch and bluegills are the prime targets, although northern pike, minnows, darters, and pumpkinseeds are commonly infected. The yellow grub has a complex life cycle. A fish parasitized by a yellow grub may be eaten by a great blue heron; the flesh of the fish is digested and the grub crawls to the throat and mouth of the bird, where it matures into an adult. The adult releases eggs, which are washed out of the heron's mouth into the water as the heron is feeding. The eggs hatch in the water into free-swimming larvae that penetrate certain species of snails. In the snail, each larva multiplies a thousandfold or more, and when a certain stage of development is reached the progeny leave the snail and become free-swimming again. These, upon contacting certain species of fish, burrow into the flesh and become yellow grubs. Light infections in the fish have no detrimental effect, but heavy infections cause the fish to swim more slowly, or may interfere with their growth. There is little danger of the yellow grub infecting man, and any parasites of this type are killed by thorough cooking. The BLACK GRUB, or BLACK SPOT (Neascus spp.), is the most conspicuous para- site of fish. The parasite appears as a small black spot in the skin, about 1 mm 38
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