This is a great skill to have – the Butterfly. If you can learn this technique on a trout it makes steelhead, salmon and bigger fish very easy. Below is a picture guide on how to cut up a round-fish (as opposed to the other common shape – the flat fish – think halibut and flounder for those)
First start with a round-fish – a trout, salmon, steelhead ect. Gut the fish and move it to a clean cutting surface. At the anal fin slice along the spine toward the tail fin.
Cut so that you expose the skin on the underside of the back of the fish. See below. Next slide the tip of the blade under the ribs of the fish. Then slowly push the knife toward the spine, working your way up each section of the fish. Repeat the knife under the ribs slide until the entire half of the fish is “ribbed” Next slide the knife along the spine, you will feel resistance from pin bones at this point. You will need to simply slice through them, removing them later on bigger fish. Repeat the process on the other side of the fish. When both sides are completly cut the bones should come up off the back skin. Cut free the meat that is still attached, careful not to puncture the skin. Cut off the tail. Butterflied Trout with bones pulled up. Cut off the head at this point. Butterflied trout with roe. Yum. Cook with this recipe.