I did some digging...
Wild fish normally carry a variety of parasites, and usually show no negative effects unless the infection is extremely heavy. Largemouth bass are commonly infected with the bass tapeworm, which lives in the intestine of bass; this species does not infect humans. Two other parasites frequently observed by anglers are the yellow grub, and the black grub or black spot parasite. The yellow grub is the larval stage of a trematode worm which forms small whitish or yellowish cysts in the flesh and near or just beneath the skin. Black grub parasites are also the encysted larvae of trematode worms, and appear as a small black spot about the size of a small pinhead, in or just beneath the skin.
Both of these parasites have a complex life cycle involving snails, fish, and fish-eating birds such as herons or kingfishers. The adult worms live in the mouth and throat of fish-eating birds, and shed their eggs into the water as the bird feeds. The eggs hatch and the free-swimming larvae infect snails. Later, advanced larvae emerge from the snail and penetrate the skin of a fish. When the fish is eaten by a bird, the cycle is completed.
While all these parasites are aesthetically unappealing, they will not infect humans and are killed by thorough cooking. There are no chemical treatments available to eliminate these parasites in pond situations. However, snails are a preferred food of redear sunfish, so establishing a good population of these fish in the pond may help disrupt the life cycle of parasitic trematodes.
We receive many inquiries each year from people who have seen or caught fish which have black spots or yellowish bumps on their fins and in their flesh. More often than not their first reaction to these diseased fish is to wonder if they are fit to eat and then throw them away. A FISH THAT IS PROPERLY CLEANED AND COOKED CANNOT TRANSMIT ANY PARASITE OR DISEASE TO PEOPLE WHO EAT THE FISH.
The most commonly observed parasites of fish are yellow grubs, black spots and tapeworms. In all these cases the parasite goes through a complex life cycle and undergoes physical changes within a variety of organisms called hosts. Most fish have parasites and they seldom affect the well being of the fish except under unusual conditions. Because most parasites have complex life cycles, attempts to control them are usually futile and unnecessary except in hatchery or fish farming situations.
Black spot is caused by a parasite called a fluke which burrows into the skin of fish. The black pigment (about pinhead size)forms in the tissue surrounding the fluke and is a reaction of the fish caused by the parasite. The fluke itself is actually a whitish color.
Yellow grub is also caused by a fluke which penetrates the skin of fish and curls up into a sac under the skin or in the muscle where it grows to be the grub. The grubs are often found in the flesh of fish near the dorsal fins. When freed from the sac the grub may be up to a half inch long.
Larval tapeworms are common in the organs and body cavity of many fishes. Because internal organs are discarded when fish are cleaned this parasite is often overlooked. Tapeworms resemble long thin ribbons about 1/16 of an inch wide.
Only three kinds of fish parasites known to occur in North America can live in humans, and none of these has ever been reported in Missouri. Furthermore, these three parasites are only problems when fish are not thoroughly cooked, but eaten raw.
So, we have to quit eating raw fish now. I am so upset - NOT!