"Chinese" Triggerfish (Balistes rotundatus)
pictured: Balistes capriscus
"'A triggerfish,' I remarked. 'A Chinese triggerfish,' Ned added. 'Genus Balistes, family Scleroderma, order Plectognatha,' Conseil murmured. No doubt about it, Ned and Conseil together could make one distinguished naturalist." (20,000 Leagues p. 98)
Triggerfish, consisting of about 40 species, are so named due to a dorsal spine that locks in place and is unlocked by depressing a "trigger" spine. They are unusually intelligent for fish; this, along with their often bright colors, makes them popular aquarium fish.
The name "Chinese triggerfish" seems only to appear in translations of 20,000 Leagues Under the Sea. What fish, then, did the travelers see? Luckily, Conseil identifies the genus, and Balistes only has eight species. Only one, Balistes rotundatus, is found in the West Pacific, where the Nautilus was traveling. My usual reference sources provide neither information, a common name, nor a photograph, so this post is illustrated with Balistes capriscus, the grey triggerfish. This triggerfish displays the coloring Aronnax describes (grey on top, white on the bottom), but it's only found in the eastern Atlantic.