But the presence of parasites is no reason not to eat fish
Although not widely discussed, most animals, including fish, are host to a variety of parasites.
Parasites rarely kill the host fish, but may weaken individuals or make consumption of the flesh less appealing. One of the most-common parasites seen locally is the so-called spaghetti worm, found in spotted seatrout. This white worm is really the larval stage of a tapeworm that infests sharks. As with many other parasites, the life cycle of this worm is amazingly complicated.
The adult tapeworm is up to eight inches long and lives in the guts of sharks. Like other tapeworms, it attaches to the stomach with sharp hooks and takes nourishment from the host. Eggs from the adult worm are passed into seawater where they hatch into tiny free-swimming larvae.
If the larvae are eaten by a small shrimp-like animal called a copepod, the larvae transform into the next life stage. The copepod in turn is eaten by baitfish, which is then eaten by spotted seatrout.
Once the larval worm is in the trout, it burrows from the digestive tract into the trout's flesh. Here it may live for several years. The life cycle is completed when a shark eats the trout and becomes host to the adult worm.
Spotted seatrout seem to develop a resistance to the worm which limits the amount of infestation. Studies have shown that in general, large, older fish have no more worms than small, younger fish. Fish from high-salinity waters often have more worms than those from low-salinity waters. Generally, spotted seatrout only have two to four worms per fish, but in filleting the fish, the worms are cut to pieces, giving the appearance of many more worms.
While the worms are not appealing, there is no reason not to eat the fish. The worms may be removed easily. Many fishermen do not even bother. The worms are killed by cooking and become unnoticeable. For those who need further reassurance, there is no record of human infection from this parasite.
Fish in general are host to many different kinds of parasites. Only a few can be transmitted to humans. Nevertheless, it is always a good practice to cook fish, despite the recent interest in eating raw fish.