Like other meats, properly cleaned and cooked fish can still transmit the basic food poisoning diseases if left out or handled improperly after cooking. Worms or grubs in fish go through a complex life cycle and undergo physical changes within a variety of organisms called hosts. Most fish have parasites and they seldom affect the health of the fish except under unusual conditions. Most fish parasites have complex life cycles often involving birds, snails, and microscopic animals. Attempts to control them are usually futile and unnecessary except in controlled hatchery or fish farming situations.
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. Black spot is caused by a parasite called a fluke which burrows into the skin of fish. The fluke itself is actually a white color. Yellow grub is caused by flukes which burrow into a fish and curl up into a sac under the skin, in the muscle or in internal organs. These flukes are often found near the dorsal fins, but occasionally in the organs.