I was looking over the 1994 review article by John Davenport (in Reviews in Fish Biology and Fisheries) on flying fish aerodynamics, and he makes a very interesting and astute observation:
"The expanded, flat pelvic fins of four-wingers have evolved, not to increase wing area, but to function as tailplanes or stabilizers well behind the centre of gravity, with an area some 20–35% of the total lateral fin area, and an angle of incidence less than that of the cambered pectoral fins."
In other words, the big forward pectoral fins, which are the main wings, are cambered and produce the vast majority of the weight support during gliding. The "hindwings", i.e. the pelvic fins, are control-related. Readers should note that the pelvic fins in flying fish are also much shorter and broader in overall shape (i.e. low aspect ratio) - this makes sense for airfoils used to control but not as primary gliding support surfaces.
Those that work with me regularly know where I am going with this, as there is another group of critters with "hindwings". More on that some other time.