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Becker, George C. / Fishes of Wisconsin
(1983)

Fish parasites,   pp. 38-42 PDF (1.7 MB)


Page 38

 
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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