from The Century Dictionary.
- noun On an English man-of-war, a small storeroom in the afterhold where fish and sometimes spirits were kept.
Sorry, no etymologies found.
It was no sooner discovered, than the fish-room was found to be full of water, and the casks in it afloat; but this was, in a great measure, owing to the water not finding its way to the pumps through the coals that lay in the bottom of the room.
A General History and Collection of Voyages and Travels, Volume 16 Robert Kerr 1784