You eat sushi, and 30 minutes to an hour later you have terrible diarrhea, stomach cramping, and maybe even, dare I mention it?…anal leakage. What’s more, your stool is orange, oily, and greasy. There is a name for this, believe it or not: Keriorrhea. It is named specifically to describe what is happening because of your sushi meal. Probably, you ordered the white tuna, but it wasn’t really white tuna.
It is quite possible that becoming sick soon after eating a meal has nothing to do with that meal, as food poisoning is not necessarily caused by the last meal you ate. But in this case, it is possible that it was the fish.
White Tuna in Japanese Sushi
White tuna is what we call albacore tuna or Thunnus alalunga. In Japan, it is called binnaga maguro or bincho maguro. On menus, it is often called Shiro Maguro, which means ‘white tuna’ and refers to its rosy cream-colored flesh. Although we have long tended to think of albacore tuna as something from a can, often called chunk white, as the popularity of sashimi and sushi continues to grow, and tuna stocks become more endangered, albacore offers certain advantages, one of which is the fish breed quickly and grow rapidly. Despite this, they are pressured just like other tuna and are threatened by over-fishing.
Fake White Tuna Can Make You Sick
But, if that was a nice fresh albacore that you were served at your sushi joint, you wouldn’t be sick. Quite likely, it was not white tuna at all. A great deal of what is being served as white tuna in the U.S., up to 84% of it, is actually a fish called escolar, a.k.a. snake mackerel. This may actually be one of two species of fish that are commonly called escolar, Ruvettus pretiosus and Lepidocybium flavobrunneum. They are banned from sale in Japan and Italy, and other countries require warnings be given.
This fish accumulates toxic wax esters called gempylotoxin, which cannot be digested in the human gut. Although not everybody is affected the same, in some people, gempylotoxin has a severe laxative effect. Symptoms may appear as early as 30 minutes or as long as 36 hours after consumption. Pain and cramping is not always present, but in susceptible people, the oily diarrhea and, heaven forbid, anal leakage often occurs. Either way, it’s a miserable experience and it can take as long as two days for symptoms to subside. It’s basically like getting a big old-fashioned dose of castor oil. Just like castor oil, gempylotoxin is a strong, purgative oil. As unpleasant as the symptoms are, they are not seriously harmful and the ‘keiorrhea’ is not likely to cause dehydration. Although ‘toxin’ is in the name, gempylotoxin, which takes its name from the fish family Gempylidae, is not really toxic.
Danger aside, the symptoms can occur without warning and can be quite hard to control. This article in the kitchn relates a particularly inconvenient reaction, involving an escalator. As the article mentions, the laxative effect can be severe enough that escolar has been nicknamed olestra fish or ex-lax fish.
You may have seen escalor offered at other restaurants besides sushi. It is sometimes mislabeled as butterfish and it is also called waloo (or walu), or king tuna. In sushi restaurants, it might be called white maguro or just white tuna. They’ve also been misidentified as various other fish like sea bass and blue cod.
Why Serve Escolar?
In all fairness, there is a reason why restaurants would want to serve escolar: It is delicious, with a buttery flavor. The effect depends on the serving size. Small servings of six ounces or less may be generally tolerated. The flesh of the fish can contain around 20% by weight of the toxic oil. So, the more you eat, the more oil you get. The more oil you get, the more likelihood that you’ll get symptoms, and the worse they will be.
Escolar is not banned in the United States. The FDA simply warns about the potential for ‘Gempylid Fish Poisoning’ or ‘Gempylotoxism’ and advises against the sale of the fish in intrastate/interstate commerce, while requesting that anyone selling or serving the fish informs their customers about the purgative effects of the oil.
Other Dangers from Raw Fish
Gempylotoxin is, of course, not the only danger posed by raw fish. Fish frequently carry parasites that can infect humans. The Japanese have high rates of nematode infection because of the level of raw fish consumption in Japan. This is much less common in the United States, but possible. The most common parasitic diseases from raw fish consumption are those caused by cestodes, trematodes, nematodes, and Myxosporidia. As the consumption of raw fish throughout the world increases, the rates of parasitic infections will increase. In 2004, the World Health Organization (WHO) estimated taht over 40-million people were infected with fish-borne trematodes, which are the most prominent species infection humans.
Blast freezing can effectively kill most of these parasites, and the USDA Retail Food Code requires it for all fish which is meant to be consumed raw, except tuna, which does not often contain parasites. As well, farm-raised fish do not often have parasites. Be aware that acids to not kill parasites, so preparing ceviche or other raw fish dishes with high acid levels does not protect from parasites. Other than freezing, only cooking will work.
Experienced sushi chefs may sometimes be able to spot visible larvae, appearing as cysts, such as those from anasakids, or larger worms such as Eustronglyides sp., but many are invisible to the naked eye.