In Frank Schaefer's Aqualog book on Poly's he states there is a bit of confusion re the max size a Rope fish will get to.
But suggests 35cm is the max one could expect in captivity.
I've had 6 now. The largest have always maxed out at about 12-13".
As far as I know, ropes are all wild caught. If they got over 12" you would think you'd see 20" ones in the stores on a regular basis.
I'll post some pics tonight.