fillet a fin ? Easy..
1) Catch fin using epoxy, glue or bright striping. Warning, some fins can really put up a struggle to get them into the boat - close to a Great White Shark for strength - just watch the sharp edge.
One tip is to use CA on the hook, a full size Fin can't refuse it.
2) Set your just captured fin on the fillet table, and use a 1/16th inch Exacto Fillet knife, with the reflex edge.
3) Skin the scales off at a 18 degree angle, repeat for the 2nd side.
Voila ! ... Instant Filletted Fin