According to an 1837 report from the Ordnance Survey Letters, the area once held the ruins of an old castle that local tradition claimed belonged to an Admiral Fish. The connection between the surname and the place name seems almost too convenient to be coincidental, though whether the admiral gave his name to the land or took his name from it remains lost to history.

The castle itself has suffered the fate of many Irish fortifications; what remained standing in the 19th century has since vanished entirely from view. When archaeologists surveyed the site in 1986, they found no visible traces above ground, marking another casualty in Ireland’s catalogue of disappeared structures. The Sites and Monuments Record file confirms this absence, leaving only historical mentions and local memory to mark where the castle once stood.

Today, visitors to Castlefish will find little to suggest its castellated past. The townland continues as rural Kildare countryside, its fields and hedgerows giving no hint of the defensive structure that once commanded this spot. Yet the place name endures, a linguistic fossil that preserves the memory of Admiral Fish’s castle long after its stones have been scattered or sunk beneath the soil.