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Home > Resources & Publications > Newsletters & Magazines > Chenier Ecology > 2007 > 7-07

Resources & Publications:  Chenier Ecology

July 2007

Spaghetti Worms in Fish

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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