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Req. help locating fish-borne parasite info

fbio1125 at vega.selu.edu fbio1125 at vega.selu.edu
Fri Aug 18 18:10:45 EST 1995

In article <407nm3$b69 at newsbf02.news.aol.com>, edesutton at aol.com (EdESutton) writes:
> I am searching for information on what I believe is a parasite I have
> found growing in fish I have caught in clear-water streamsm in the
> South-Western corner of Missouri.  These parasites(if that's what they
> are) are found in the flesh of the fish, usually growing just beneath the
> skin, and resemble small yellowish-tinted maggots.  The skin of these fish
> is sometimes disclored a little directly above the locations where these
> parasites are growing.  Initially I though they might be small fatty
> deposits in the fish flesh, but I have dug them out and they are alive and
> they wiggle around like little grub-looking-things.  The fish species I
> most often find them in is small mouth bass. 
> I apologize in advance if this is not the proper place to post such a
> message. However, I was hoping someone might be able to point me in the
> right direction to find this information.

It is difficult to say exactly what your parasite is without actually seeing a
specimen, but your description is detailed enough to make me think that you
have encountered a type of flatworm parasite called a fluke.  In fact, the
particular fluke that you have found is probably one called "the yellow grub"
and belongs to the genus Clinostomum.  If this is the case, then you might be
interested in the following information concerning this fluke.  It has a three
host life cycle involving a snail, a fish, and a fish-eating bird.  The
parasites are released from the snail as a juvenile stage that is so small that
they are not visible without using a microscope.  These parasites swim from the
snail and if they encounter a fish they burrow into the flesh and form a thin
cyst wall around themselves.  In time they grow to the size that you observed. 
Probably in the process of removing them from the fish you ruptured the cyst
wall and observed the fluke writhing actively.  Although the parasite has grown
in the fish, it is still a juvenile, not sexually mature.  To reach sexual
maturity, the parasite must develop in a bird, and herons (which eat fish) are
probably the host in which this maturation occurs.  These sexually mature worms 
produce eggs which leaves the heron via the feces.  If the tiny little parasite
in the egg hatches and encounters a snail, then the snail becomes infected,
thus completing the three host life cycle.

Since humans are not a suitable host for this yellow grub, there is no danger
of becoming infected from this particular parasite.  Besides, cooking the fish
kills the parasite, giving you double protection.  So, as you are fishing,
enjoy the marvelous biological events that are occuring around you, and by all
means enjoy your smallmouth bass dinner.  Welcome to the wonderful world of

If you have any follow-up questions, please contact me at the address below.

Bill Font
Southeastern Louisiana University
wffont at selu.edu

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