We do it a little different. 1st a knife with a piont, slip in the poo hole blade pionting to the head.
As the blade tip goes up towards the head inside and hit the breastplate mic part of the blade. Leaver the tip of the knife against the back bone, and go thru the breast plate.
Quick cut with fish still laying down across the throat.
this then enables the tip of the knife slice the bottom of the gill away.
Smaller fish can pull gills and gut out as illustrated but larger fish, the gills can be very abrasive to the hands and the top end of the gills hard to pull away clean.
So on larger fish, cut the bottom if the gill away then with tip of the knife a good knick, or if lucky slice the top of the gill anchor and pull away.
Gutting thru the breast plate kills the butt to middle of the knife edge very quick.. sSo do this at the end of filleting and skinning, not during.
And when sharpening the knife (my edges are stroped convex) with the filleting / point about 22 deg and the main blade 30/35 deg.. The 22 deg gives fine 'peel away' but not robust to cutting bones. And the 30/35 deg far more robust to keeping an edge for bpin bones and skinning.
Aski any chef, butcher etc, be it fish lamb , beef , the sweetest most tender meats are next to the bone... ie back strap, chops cheek , wings, fish forehead...
And another hint.. gutting at sea.. assuming a bait board.. fix a insert into the bait board to raise the floor up. that way you can cut straight into the fish rather than over the edge.
I leave an 1" or so at the back of the board for sinkers etc.
I used to have a wooden insert, great, this board have one of those white plastic chopping board trimmed to fit.
Dont use the plastic chopping boards, they kill the edge on knives very quick... big mistake yet to fix.