The world’s most famous fish sandwich begins as one of the ocean’s ugliest creatures. Filet-O-Fish, like many of the fish patties used by fast-food chains, is made predominantly from hoki, a gnarly, crazy-eyed fish found in the cold waters off the coast of New Zealand. In the past, McDonald’s has purchased up to 15 million pounds of hoki a year, each flaky fillet destined for a coat of batter, a bath of oil, a squirt of tartar, and a final resting place in a warm, squishy bun. But it seems the world’s appetite for this and other fried-fish sandwiches has proved too voracious, as New Zealand has been forced to cut the allowable catch over the years in order to keep the hoki population from collapsing. Don’t expect McDonald’s to scale down Filet-O-Fish output anytime soon, though; other whitefish like Alaskan pollock will likely fill in the gaps left by the hoki downturn. After all, once it’s battered and fried, do you really think you’ll know the difference?