One of the questions that people often make is what exactly is inside a Filet of Fish sandwich at McDonald's. The NY Times apparently has found out the Hoki fish, aka Whiptail is the largest source. With 15 Million Pounds being exported by New Zealand.
"One of the most popular is the hoki, or whiptail, a bug-eyed specimen found far down in the waters around New Zealand and transformed into a major export. McDonald’s alone at one time used roughly 15 million pounds of it each year." via NY Times