Eating contaminated shellfish is the main cause of food poisoning involving fish. Oysters, which are mostly consumed raw, are a good example. They usually contain bacteria that could cause food poisoning or other related conditions. Bacteria that live in water enter the body of the fish as they filter algae and sea weed. These bacteria then live in the fish and cause food poisoning.

Types and Causes of Fish Food Poisoning

There're different types of food poisoning from fish categorized by the kind of fish or toxin that causes the problem. Fish types like oysters or mussels that can be eaten raw are usually more likely to cause food poisoning. Fish poisoning is caused by consuming fish contaminated by toxins, bacteria, viruses or parasites.

1.         Ciguatera Poisoning

This is caused by consuming warm water ocean fish containing ciguatera toxin. Ciguatera is produced by a dinoflagellate - a small organism that attaches to algae in warm ocean water reefs. Small fish eat these algae and accumulate the toxin in their bodies, which is then concentrated in large predator fish. Fish containing the toxin do not change in taste, odor or appearance. Ciguatera is not destroyed by refrigeration, cooking or freezing.

The following symptoms can occur 2-12 hours after consuming the fish:

• Nausea
• Abdominal cramps
• Vomiting
• Severe and watery diarrhea

Immediately after developing these symptoms, you will experience strange sensations including:

• Your mouth tastes like metal
• Headache
• Your teeth feel loose and about to fall out
• Low blood pressure and low heart rate in severe cases
• Confusing hot and cold flashes on your body

These symptoms may be worse if your meal was accompanied by alcohol.

2.         Scombroid Fish Poisoning

Scombroid poisoning can be caused by ingesting spoiled non scrombroid fish like sardines, bluefish, marlin and mahi mahi or fish from the scombridae family including mackerel, bonito and tuna. Histamine and other similar substances cause this kind of food poisoning from fish. If the fish dies and is not refrigerated immediately, bacteria make large amounts of the toxin in the fish.

Symptoms that occur soon after you eat the fish include:

• Vomiting
• Extreme skin reddening on the face and body
• Flushing
• Chest tightness, wheezing and other chest problems in severe cases
• Hives and itching
• Bitter taste
• Nausea

3.         Shellfish Poisoning

Dinoflagellates build up on some sea foods and make poisonous substances. Despite there being many types of shellfish poisoning, the well-known types include neurotoxic shellfish poisoning, amnesic shellfish poisoning and paralytic shellfish poisoning.

• Neurotoxic shellfish poisoning has the same symptoms as ciguatera poisoning, but lasts a few days and is less severe.
• Paralytic shellfish poisoning cause difficulty in walking, talking, moving or breathing in severe cases. Symptoms last only a few days.
• Amnesic shellfish poisoning causes abdominal cramps, vomiting, and diarrhea, that occurs a day after consuming spoiled shellfish. Confusion, amnesia and coma follow in severe cases with the amnesia being permanent sometimes.

How to Deal With It

Mild food poisoning from fish can be treated at home. Plenty of liquids and bed rest will help. Ensure to replace minerals and vitamins lost due to food poisoning. Add a sachet of rehydration salts to your drinking water to replace them and keep hydrated as dehydration is a major risk of food poisoning. In case you get dehydrated, seek medical attention.

Seeing a doctor is a must if you develop ciguatera food poisoning. However, there is no particular antitoxin against ciguatera toxin.

• Some researchers suggest inducing vomiting for someone who has consumed ciguatera contaminated fish within the last 3 to 4 hours if they are still awake and alert. Ipecac was suggested as a medication to induce vomiting, but it was found to cause too much dehydration.
• Some physicians currently recommend activated charcoal for gastrointestinal decontamination. Activated charcoal can absorb the toxin if administered 3 to 4 hours after ingestion.
• Stay hydrated. Intravenous fluids could be required if you experience nausea and vomiting.
• Symptoms can be reduced by osmotic diuretics like mannitol (Osmitrol). Gabapentin and amitriptyline may help reduce neural pain symptoms. You could use hydroxyzine and Diphenhydramine to relieve itching. NSAID’s and acetaminophen like Tylenol may be used to reduce pain.
• Keep off fish, nuts, alcohol and nut oils upon exposure to ciguatera toxin as they could trigger recurrent symptoms.

When to Call a Doctor

If the following symptoms last more than 3 days, consult a doctor:

• Fever
• Dehydration signs like dry mouth, dizziness, decreased urination fatigue, or increased heart rate or breathing rate
• Dark stools or bloody diarrhea
• Severe pain in the belly
• Prolonged bloody vomiting

How Can I Prevent from Getting It?

Food poisoning from fish can definitely be prevented. The following measures could help:

• Avoid storing fish especially shellfish in water
• Refrigerate fish immediately after purchase
• Avoid mixing raw fish with cooked fish
• Always clean your hands before and after handling fish. Clean your working surface, kitchen work tops, utensils and chopping boards.