Many thanks to Kilchoan fisherman Justin Cameron for allowing his picture of a marine goldfish to be used by the Diary. He found it in one of his prawn creels just to the west of the pier, at a depth of about 25 fathoms.
The Diary is no expert on marine fish but Google suggests it's a boar fish, Capros aper, also known as the Zulu fish. It's uncommon in shallow water, preferring depths of around 100m, so it's out of its habitat sitting in a creel. There's an interesting page about it here.