Wow! That very simple knife must have laid in someone's drawer for decades without seeing the light of day. I'm getting to be an old enough codger to realize that plated steel was a desperate effort by utility manufacturers to counter the 'stainless' revolution that began sweeping the world in the late 1950s. I was gifted a 1958 wedding set of plated steel Sheffield-made carving knives many years ago and thoughtlessly threw them out. Carbon steel was still out there in the late 60's but disappearing fast. I presume this fish knife is now become a collector piece but if it were mine I'd be using it!
My long time kitchen joy is a wood handled hand ground carbon steel butter knife, likely from the 20's-30s, that says 'Sabatier Seal made in France' on it. Would have been a cheap import and likely have died a long time ago if the farmhouse where I discovered it had had an automatic dishwasher.
I love using the oldies. Whenever it gets too stained or discoloured I shine it up with 1500 grit sandpaper.