By Elder Paisios the Athonite
Every Christmas, the elder would get a herring for the joyous Twelve Days of Christmas, since there is a dispensation for fish for the feast. He did not, however, throw away the backbone of the fish, but hung it by thread on a nail. On feast days of the Lord or the Mother of God, he would boil a little water in a tin can, dip the fishbone two or three times in the water so that it took on a bit of a smell, and then throw in a little rice. In this way, he observed the dispensation for fish but also condemned himself for eating fish soup in the desert! Then, he would hang the backbone on the nail again for the next dispensation, until it became quite white and only then would he throw it away.
From Athonite Fathers and Athonite Matters, p.33.