| This
month’s article was sparked by a couple of phone calls
questioning the safety of consuming fish with worms in the
flesh.
Spaghetti
worms are common parasites of saltwater fish in the Sciaenid
or drum family, which include speckled and white trout,
black drum, redfish and croakers. Most commonly known as
spaghetti worms, each fish actually has a specific parasite
which prefers its flesh. Most common in sea trout is Poecilancistrium
caryophyllum. Worms found in black drum are most often Pseudogrillotia
pIeistacantha.
Finding
worms in their freshly caught fish fillets can be quite
unsettling to some fishermen. However, they pose no human
health risk.
In speckled
trout the worms are most commonly found in the middle of
the fillet below the dorsal fin, while in black drum they
are more commonly found near the tail end of the fillet.
While the idea of worms in fish is unappealing, cooking
kills them. No human infections have been recorded, and
researchers have been unable to infect warm-blooded animals
with the parasite. Although not necessary, some fishermen
prefer to remove the parasite by squeezing the end of the
worm between a knife blade and the thumb and pulling.
Spaghetti
worms are actually parasitic tapeworms of sharks, which
are using the trout or drum as an intermediate host.
The
cycle begins with eggs produced by an eight-inch long adult
worm living in a shark's intestine. After being passed into
seawater, the egg hatches into a tiny swimming larva called
a coracidium. If this larva is eaten within two days by
a small marine crustacean like a copepod, it develops into
another stage called a procercoid. At this stage some uncertainty
exists as to what happens. The copepod may be eaten by a
trout, passing the larval worm on to the trout. However,
since small animals like copepods are seldom eaten by larger
trout, and since few trout less than 10 inches long have
spaghetti worms, another host is suspected.
More
than likely, a small bait fish like an anchovy eats the
copepod and it in turn is eaten by the larger trout. In
any case, once the larval worm is in the trout's digestive
tract, it tunnels its way into the trout's flesh where it
may live for several years. The life cycle is completed
when a shark eats the trout and serves as host for the adult
worm.
Research
has shown that approximately 40 percent of Louisiana and
Mississippi speckled trout are host to spaghetti worms,
with an average of between one and two worms occurring per
fish.
The
number of trout carrying worms seems to be directly related
to the characteristics and quality of the water in which
the trout live. In general, the saltier the water and the
less polluted it is, the higher the levels of infection.
This may be due to either one of the intermediate host's
or the larval worm's needs for saline, unpolluted waters.
Another
interesting fact is that once a trout becomes host to one
or several spaghetti worms, it seems to develop immunity
to further infections. If this were not the case, large,
old fish would have many more worms than a 12- or 14-inch
fish.
More
information is available at www.seagrantfish.lsu.edu/resources/factsheets/spaghettiworms.htm.
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