Escolar is a type of fish whose muscle tissue can naturally contain approximately 20% by weight of an indigestible oil made up of high amounts of wax esters. This oily substance is named gempylotoxin, after the family of fish, Gempylidae, that escolar belongs to. Humans are unable to digest the wax esters in gempylotoxin, thus they pass through the gastrointestinal system. Although its name suggests otherwise, gempylotoxin is not toxic to humans, but is indigestible, having a laxative effect which can cause dramatic, short-lived gastrointestinal responses in some people. Gempylotoxin is considered to be naturally derived from the fish's diet.
Escolar is the common name for two species of fish, Ruvettus pretiosus and Lepidocybium flavobrunneum. Other common names for these fish species are snake mackerel (both species) and oilfish«(R.pretiosus only). Both R. Pretiosus and L. Flavobrunneum have been misidentified and mislabeled as gemfish, rudderfish, butterfish, sea bass, blue cod, ruddercod and walu.
Escolar is found worldwide in tropical and temperate waters. It can be legally imported into Canada and is most frequently sold frozen or served in restaurants.
Although gempylotoxin is indigestible by humans, not everyone that consumes escolar experiences undesirable symptoms. When these undesirable symptoms do occur, onset generally takes place a few hours following escolar consumption and ceases within 24 to 48 hours. Symptoms, in those who experience them, can include one or more of the following: the rectal passage of an oily yellow or orange substance (called keriorrhoea), diarrhea, nausea, vomiting, abdominal pain, and headache. Kerriorrhoea is not associated with a loss of bodily fluids and is not considered life threatening.
The Canadian Food Inspection Agency (CFIA) works to ensure that escolar is not misidentified or mislabeled when it is sold at the retail level.
Although escolar can elicit undesirable symptoms in some people, it does not pose a health risk to consumers; therefore, Health Canada continues to allow escolar to be sold on the Canadian market.
In 2007, Health Canada released the revised version of Eating Well with Canada's Food Guide. The Guide recommends eating at least two 75 g servings of fish each week and suggests consuming species that are high in omega-3 fatty acids, such as char, herring, Atlantic mackerel, salmon, and sardines.
Ensure that you know what species of fish you are eating. Consumers often report the adverse reactions described above following the consumption of misidentified and mislabeled fish species. Purchase fish from reputable sources and confirm the species of fish with the retailer or restaurant owner if you are in doubt.
While heating does not affect the gempylotoxin, preparing escolar in such a way that as much oil as possible is removed (i.e.: grilling) may reduce the onset or magnitude of adverse gastrointestinal symptoms.
There appear to be individual differences in sensitivity to gempylotoxin, but these differences have yet to be characterized due to a lack of information. It is not known whether certain population subgroups may be more susceptible than others to adverse effects associated with gempylotoxin exposure. Nevertheless, caution is advised for sensitive groups such as pregnant women, children, the elderly, and those with bowel or absorption problems. Such individuals are advised to avoid the consumption of escolar. Limiting the amount of escolar consumed could reduce the severity of undesirable gastrointestinal symptoms, although there is insufficient information available to establish an intake level that would prevent the onset of such symptoms. It is recommended that people consuming escolar for the first time consume small portions so that they can determine their susceptibility to any negative effects from gempylotoxin. What is considered to be a 'small portion' varies between individuals. Health Canada's review of Canadian fish consumption figures estimate that the average adult portion size of a finfish meal is 150 g.
Histidine and mercury are two other types of compounds that can be present in escolar and have the potential to pose a health risk to consumers.
Certain types of fish, including escolar, naturally contain high levels of histidine, a naturally-occurring amino acid. Histidine can be converted to histamine under conditions of improper storage. Histamine can trigger a severe allergic-like reaction in humans when consumed in high doses - this is commonly referred to histidine or scombroid poisoning. For more information about histidine poisoning refer to the links in the "For More Information" section, below.
Escolar, as well as other predatory fish, have been identified to contain relatively elevated levels of mercury. Health Canada has developed a 1.0 ppm standard and has also issued consumption advice for escolar, as well as other types of predatory fish, in order to minimize the amount of mercury that Canadians are exposed to from fish. The advice includes information to help Canadians make healthy fish choices. The "For More Information" section, below, includes links to additional information about mercury in fish.