ANSWER: Sonny, you scooped up a scrawled filefish, Aluterus scriptus. You were pretty astute in thinking this was a triggerfish; filefishes and triggers are closely related, often put in the same family. But the filefishes, as you mention, are very thin, and they have only two dorsal spines, whereas the triggerfishes have three. Although their mouths are tiny, they do have formidable teeth. The species you caught was not lost, and in fact is found worldwide in tropical and temperate seas. They are sluggish swimmers, preferring to ride with the currents, but favor some sort of cover, such as the weed line where you netted it. Often, swimmers in the surf who encounter small mats of sargassum washing in can shake out other, smaller species of filefishes that live there.
To me, the scrawled filefish is beautiful, with its striking colors, but also strange-looking due to its odd-shaped head and body. Of the 10 species of filefishes that occur in the Gulf, this species is the largest, sometimes approaching a surprising 3 feet in length, while many of the other species rarely exceed a foot. For those few filefish that reach a decent size, I've found the fillets to be very tasty, but so thin that they can be overcooked quickly.
— Bob Shipp