What is this strange kitchen implement?

It’s a filet knife so you don’t have to go get a second tool to filet the fish once you’ve finished scraping the scales off:

http://www.foodclassics.com/store/cat/collectables-homeware-kitchenware-cutlery/17/Vintage-Combination-Filet-Knife-Fish-Scaler-Sweden-260633856954.html

Thanks, Baracus!

That would be the worst filet knife ever made, then, as a filet knife needs to be flexible. It’s also too short. You can’t tell which side of that blade is sharpened, but my money is on the inner curved portion, which would make it a gutting knife, and which makes more sense.

i don’t think you could scale a fish in one pass either.

And I was going to ask whether there was a small blue plaque by the door saying H R Giger slept here

I agree but even so even if I owned one I wouldn’t use for scaling either. This coming from a gal that’s scaled and gutted hundreds of fish over the years.

As soon as I saw it, I thought “grapefruit tool,” but on the other hand, it has more parts than it needs to.

So do I. But then again, “Grapefruit Tool” was my nickname on Tool Academy.

I am intrigued. Please provide complete details.

Think “Industrial Scale”. It would be a specialized tool, made inexpensively, for use in commercial fish packing to get the job done fast, if not necessarily to the standards you might use in your own kitchen.

The back part is to gut the fish. You would slice it into the stomach and pull up. Usually a hooked knife is for slicing open a fish belly.