How to Debone a Whole Fish
from https://weekendatthecottage.com/

Step One: Cook the fish. This method of deboning a whole fish will work on fish that has been poached, oven roasted, panfried or grilled.

Step Two: Remove the head and tail. To begin the deboning process, gently remove the head of the fish by cutting into the flesh following the curve of the gill cover. Carefully pull the head away. On the opposing end of the fish, cut the tail, also known as the caudal fin, and gently pull it away from the fish. Discard both.

Step Three: Remove the fins. Fish have a series of fins running along the top and undersides of their bodies. Using a fork, gently pull them free from the flesh. They come away with little effort, almost like plucking them off the meat.
Step Four: Centre Cut. Fish have a central run of vertebrae, the backbone, that runs lengthwise through the centre of the fillet. Using a sharp knife or straight butcher’s blade, carefully cut through the flesh of the top fillet on both sides of the spine from one end to the other.

Step Five: Move flesh. The next step is to gently nudge the cooked flesh off of the vertebrae and bones. We find the flesh moves easily and a fork is an excellent tool to accomplish this. Push the flesh so that quite a bit of the backbone is revealed.

Step Six: Remove bones. The next step is to gently nudge the cooked flesh off of the vertebrae and bones. We find the flesh moves easily and a fork is an excellent tool to accomplish this. Push the flesh so that quite a bit of the backbone is revealed.

Step Seven: Reassemble. The final step is to reposition the two pieces of flesh that were coaxed away back in place. Prepare to be amazed at how simple this step is. The fish seems to come back together almost by magic and your perfectly deboned cooked fish is ready to be enjoyed. Add a squeeze of lemon, a sprinkle of salt and a few slices of lemon for garnish and you’re good to go.