Hmm. I got flint with a perch, I just assumed I picked it up off the shore.

The small level number on the fish matters..
When you prepare it into food
then a level 1 fish will give you x amount fish, while a level 2 fish will give you even more fish when its chopped up.

Yeah had this happen a few times with the bonus resources, got Ooze from Giant Herring, Chitin from Coral Cod, Tin from either Pike or Trollfish, Flint from Perch, and something else may have been Black metal from Grouper or something.

If I understand it correctly Its kind of like stars for land creatures. These are both perch. one is a level 1 perch the other is level 2. The level 1 is weight 2 quantity 1. The level 2 is weight 4 quantity 2.
https://steamcommunity.com/sharedfiles/filedetails/?id=2941891313

https://valheim.fandom.com/wiki/Fish it says it gives 1 to 2 tin ore / ruby / chitin / seeds tho?

When you successfuly catch a fish, there's a chance for it to also give you random materials dependant on the type of fish( and therefore the biome.

This was implemented fairly recently in the same patch that gave us access to being able to finally make the dverger doors ourselves, and also the fishing hat.

It appears that, per the table in the wiki the bonus materials chance to occur seems to range from ~3 to ~16 % depending on the material.

what the??? never had it happen before, interesting.