Nah I tried that once a bread knife.. got thrown aside before even got thru the breast bone.
A good solid knife.. long enough to put thru the poo hole, edge side up.. slide to the breast bone with the tip right up on the skull, and simply lift hard.. the blade is at a steep angle to the breast bone, so as lift it 'slides' down the blade.
Bigger fish bigger knife.. mainly so can get the distance from bottom of breast bone to the skull.
Sharpening .. well dont have to be too fussy.. the 30 deg means edge doesnt break off easy.
Its like going to cut gum or manuka with a chainsaw, steep 30 deg for the hard wood...pine 22 deg.. If use 22 deg then the blade will only last a couple cuts on the hard wood.
If use the 30 deg on the pine , takes smaller cuts and therefore goes thru the log a little slower.
On a cheap knife its not worth the time or effort to use a stone or strop.. a drag thru is all you need.. and maybe finish with a roller ceramic if fussy..
The saw edge..
Well you are onto something there as well.
These cheap stainless , sort stay sharp knives do so because of the cheap stainless where the carbon and impurity crystals in the alloy are larger than normal.
On a microscopic level , as you use the edge, these fall out of the edge making it serrated.. and when they fall out they leave broken glass like serrated edge, which is like a microscopic saw.
I dont use these knives for filleting unless filleting a KY or something for bait on the bait board.
My good knives are left at home stored in a block.. 2 for visitors , my 2 for me only.. and the cast cleaver for what ever