I can hear from customers about white tuna. I stopped to sell this fish almost 4 years ago. This is not tuna, is Escolar. Many people still don't know about fish and they just belive in what sushi chefs say.
I got some article for you.
Perhaps you've seen this fish at your local fishmonger or on the menu at restaurants. Sometimes it's under the name "butterfish," "oilfish," or "waloo/walu." Sushi restaurants occasionally serve it as "super white tuna" or "king tuna." Maybe you've heard it's extremely tasty. This is true; escolar is delicious. It's buttery and succulent. But before you eat it, there is something important you need to know.
Escolar has been popping up on restaurant menus and in seafood markets as of late. With some varieties of fish in danger of being overfished and other species becoming undesirable due to their high mercury content, seafood purveyors need a fish that's delicious, cheap, sustainable, and low in mercury. Escolar fits the bill as it is economical and politically correct, but it comes with a side effect that fishmongers and waiters fail to mention.
Escolar is a type of snake mackerel that cannot metabolize the wax esters naturally found in its diet. These esters are called gempylotoxin, and are very similar to castor or mineral oil. This is what gives the flesh of escolar its oily texture. As a result, when full portions of escolar are consumed, these wax esters cause gastrointestinal symptoms.
To be frankly and bluntly specific - and I'm sorry for this - consumption of escolar causes explosive, oily, orange diarrhea. People have reported that the discharges are often difficult to control and accidents can happen while passing gas. I personally know someone who ate an escolar steak one night, unaware of its side effects. The next day he was riding the elevator to his office when out of nowhere his bowels unleashed a surprise attack on his pants. As he said later, "Thank God I had my gym bag with me, which had a clean pair of underwear in it." This explains why escolar is also called the "olestra fish" and the "ex-lax fish."
The Japanese and Italian governments have banned the importation and sale of escolar for these reasons. The governments of Canada, Sweden and Denmark require that all escolar come with warning labels. The FDA lifted the escolar ban in 1992 because the fish is nontoxic - sure, it causes embarrassing things to happen in your pants, but it won't hurt or kill you.
In spite of all this, escolar is indeed very buttery and delicious, and should be enjoyed, but never in portions larger than six ounces. Portions below six ounces will not cause gastrointestinal distress. Don't say we didn't warn you.