Poisoning - fish and shellfish Health Article

Definition

This article describes a group of different conditions caused by eating contaminated fish and seafood. The most common of these are Ciguatera poisoning, Scombroid poisoning, and various shellfish poisonings.

This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as 911) or the National Poison Control Center at 1-800-222-1222.

Alternative Names

Fish poisoning; Dinoflagellate poisoning; Seafood contamination; Paralytic shellfish poisoning; Ciguatera poisoning

Poisonous Ingredient

In Ciguatera poisoning, the poisonous ingredient is ciguatoxin. This is a poison made in small amounts by certain algae and algae-like organisms called dinoflagellates. Small fish that eat the algae become contaminated. If larger fish eat a lot of the smaller, contaminated fish, the poison can build up to a dangerous level, which can make you sick if you eat the fish. Ciguatoxin is “heat-stable." That means it doesn’t matter how well you cook your fish, if the fish is contaminated, you will become poisoned.

In Scombroid poisoning, the poisonous ingredient is histamine and similar substances. Normal bacteria on these fish create large amounts of this toxin after the fish dies if it is not immediately refrigerated or frozen.

In shellfish poisoning, the poisonous ingredients are toxins made by algae-like organisms called dinoflagellates, which build up in some types of seafood. There are many different types of shellfish poisoning. The most well known types are paralytic shellfish poisoning, neurotoxic shellfish poisoning, and amnestic shellfish poisoning.

Where Found

Ciguatera poisoning normally occurs in larger fish from warm tropical waters. The most popular types of these fish that are eaten include sea bass, grouper, and red snapper. In the United States, the waters around Florida and Hawaii have the highest potential for contaminated fish. The risk is greatest in the summer months, or any time a large amount of algae are blooming in the ocean, such as during “"red tide." A red tide occurs when there is a rapid increase in the amount of dinoflagellates in the water. However, today’s transportation means that anyone around the world may be sitting down to a dinner from a fish from contaminated waters.

Scombroid poisoning usually occurs in large dark meat fish such as tuna, mackerel, mahi mahi, and albacore. Since this poison develops after a fish is caught and dies, where the fish is caught doesn’t really matter. The main factor is how long the fish sits out before being refrigerated or frozen.

Like Ciguatera poisoning, most shellfish poisonings occur in warmer waters. However, poisonings have occurred as far north as Alaska and frequently in New England. In addition, most shellfish poisonings occur during the summer months. You may have heard the saying “Never eat seafood in months that don’t have the letter R." This includes May through August. The number of poisonings also increases when there is a "red tide." Shellfish poisoning occurs in seafood with two shells such as clams, oysters, mussels, and sometimes scallops.