Enter the escolar.
A tasty mackerel that has recently come into vogue in trendy bistros (and, apparently, in eateries as well), escolar is a by-catch of tuna fishing, meaning that it ends up in the nets more or less accidentally. A wary eye on the bottom line has led tuna fishermen to hawk these incidental escolar to merchants who wish to impress restaurateurs with the latest cutting-edge fish.
On the surface, it all seems innocent enough. Escolar is cheap and has a buttery, meaty texture similar to that of sea bass. Its rich flavor complements the frivolous, fruity sauces everyone wants in summer. But before you order it, take heed: Not only is can it induce histamine poisoning (along with tuna and mahi-mahi) if mishandled, escolar contains high levels of an indigestible substance called gempylotoxin. This stuff is described by the FDA (which sternly recommends against escolar importation) as "a strongly purgative oil." Escolar, it turns out, is known in some circles as "the Ex-Lax fish."
You may take it from me, my friends, that the above is a gross understatement. Without going into unseemly detail, let me say that two highly disagreeable hours after my own encounter with an escolar, I had gotten my come-outtance. Don't let my involuntary impairment have been in vain. Give the escolar (and the sea bass) a miss.