Understanding the Problem: Indigestible Wax Esters
Escolar ($Lepidocybium$ $flavobrunneum$) and oilfish ($Ruvettus$ $pretiosus$) are the primary culprits behind digestive distress associated with certain oily fish consumption. These fish species, which belong to the Gempylidae family, are known to contain high levels of wax esters, an oil that humans cannot metabolize. The specific type of oil found in these fish is sometimes referred to as gempylotoxin, named after their family. While not a true toxin, this substance has a powerful laxative effect.
Unlike the beneficial omega-3 fatty acids found in other oily fish like salmon and mackerel, these wax esters pass through the human digestive system without being absorbed. As the oil moves through the intestinal tract, it can accumulate in the rectum, leading to the characteristic symptom of keriorrhea—an oily, yellow or orange discharge. Symptoms can range from mild anal leakage to severe diarrhea, often accompanied by abdominal cramps, nausea, and headache.
The Symptoms and Onset of Keriorrhea
The onset of symptoms can be unpredictable, appearing anywhere from 1 to 90 hours after consumption, though typically within 2 to 36 hours. The severity of the reaction depends on several factors, including the amount of fish eaten, the individual's sensitivity, and the fish's wax ester content. Some people may experience no symptoms, while others are highly susceptible. The condition is generally not life-threatening and resolves on its own within one to two days. It is important to note that unlike other forms of food-borne illness, keriorrhea does not cause significant fluid loss.
Symptoms of Keriorrhea
- Oily, orange discharge: The most distinctive symptom is the leakage of an oily, colored substance from the rectum.
- Gastrointestinal discomfort: This can include stomach cramps, loose bowel movements, and nausea.
- Headache: Some individuals report headaches associated with the digestive distress.
The Challenge of Mislabeling
A major issue is that escolar and oilfish are frequently mislabeled and sold under more appealing or familiar names in restaurants and stores. This deceptive practice makes it difficult for consumers to know what they are truly purchasing. Common aliases for escolar include "white tuna," "super white tuna," "Hawaiian butterfish," "walu," and "sea bass". While albacore is sometimes legitimately called "white tuna," the mislabeling of escolar is a widespread issue that has prompted warnings from food safety authorities worldwide. For example, the FDA in the US and food safety bodies in Canada and Australia have all issued advisories regarding mislabeled escolar. Some countries, like Japan and Italy, have gone so far as to ban the import and sale of these fish entirely due to the health concerns.
How to Avoid Getting Sick
The best way to avoid keriorrhea is to be aware of the risks and take preventative measures. When purchasing or ordering fish, always ask for the specific species and be wary of generic or ambiguous names like "white tuna" or "butterfish". If eating out, confirm with your waiter that the "white tuna" is indeed albacore and not escolar. The most effective strategy is to avoid escolar and oilfish altogether, but if you do choose to eat them, take precautions.
Tips for Safer Consumption
- Limit your portion size: Consuming smaller portions, ideally less than 6 ounces (170 grams), can reduce the likelihood and severity of symptoms.
- Trim the fattiest parts: The oil content is often higher in the belly and near the head. Choosing portions closer to the tail may help.
- Grill or broil: Preparing the fish in a way that allows the oil to drain, such as grilling, may help remove some of the problematic wax esters. However, this is not a guaranteed fix.
- Discard cooking liquid: Do not use the liquid from cooking these fish in sauces or other dishes, as it will be saturated with the indigestible oil.
- Source reputably: Purchase fish from suppliers you trust who can verify the species you are buying.
Escolar vs. Other Oily Fish
It's important to distinguish between escolar and other oily fish that are safe and nutritious. The health benefits of fish like salmon, mackerel, and herring are well-documented, primarily due to their high content of digestible, heart-healthy omega-3 fatty acids. Escolar's high fat content is comprised of indigestible wax esters, making it fundamentally different despite its buttery taste.
| Feature | Escolar/Oilfish | Common Oily Fish (Salmon, Mackerel) |
|---|---|---|
| Fat Content Type | Indigestible wax esters (gempylotoxin) | Digestible omega-3 and other fatty acids |
| Digestive Impact | Can cause keriorrhea, oily diarrhea, and cramps | Generally beneficial for heart and brain health |
| Mislabeling Issues | Commonly mislabeled as "white tuna," "butterfish" | Less prone to mislabeling, standard fish names used |
| Health Effects | Acute, though temporary, gastrointestinal distress | Positive health benefits, including reduced inflammation |
| Availability | Banned in some countries (Japan, Italy), restricted in others | Widely available and recommended for regular consumption |
Conclusion: Making Informed Choices
The answer to the question, "what is the oily fish that makes you sick?" points directly to escolar and oilfish. While the risk is not life-threatening, the potential for severe digestive upset is high and often unexpected due to widespread mislabeling. By being an informed consumer, asking the right questions, and exercising caution, you can easily avoid this unpleasant experience. It is always wise to prioritize trusted seafood sources and understand the difference between healthy, beneficial fatty fish and those that can cause problems. For more information and official advisories, you can consult sources like Health Canada, which provides a useful fact sheet on escolar and adverse reactions.
Identifying Escolar and Oilfish
Key Identifiers for Visual Confirmation
It can be difficult to identify these fish when they are filleted, but there are some traits to look for if you see them whole:
- Escolar: Dark brown skin that turns black with age, large eyes with distinctive rings, and a prominent lateral keel near the tail.
- Oilfish: Also dark in color and part of the same family, sharing many physical characteristics.
Safe Cooking Practices
While cooking does not destroy the wax esters, some preparation methods can minimize the oil content and therefore the risk of keriorrhea. Grilling, for example, allows some of the oil to be cooked away. Discarding the cooking juices is also a recommended practice. Freezing does not affect the wax esters.
The Role of Reputable Suppliers
Buying fish from reputable suppliers who adhere to proper labeling standards is crucial. This not only helps you avoid escolar but also protects you from other food safety concerns like mercury contamination, which can also be an issue with some deep-sea predatory fish. Knowing the origin and specific species of your seafood is the best defense against unexpected side effects.
