If you're lucky enough to get your hands on some really fresh katsuo, then there's no second-guessing what to do with it. Serve it as sashimi! It's very rich in iron, so I especially recommend this fish for the ladies.
For condiments, I recommend grated garlic and grated ginger.
It's hard to see, but in this photo, I'm slicing along either side of the back fin. (You might be able to see it better in the photo for the recipe for preparing Inada Fish?)
Starting from the tail end, grab the fin with your hand and pull toward the head end to remove.
There are tough scales around the pectoral fin, so scrape those off with a knife. It's hard to see here, so once again, refer to the photos for preparing Inada Fish.
There are some tough scales around the ventral fin on the fish's belly as well, so scrape those off.
Once you've finished scraping off the scales, in order to remove the head, insert your knife into the fish under the ventral fin, and push it in until it hits the spine.
Lay the fish on its side, and insert the knife under the pectoral fin, again pushing it in until it reaches the spine. Turn the fish over and repeat this incision on the other side. The head still won't come off quite yet.
Next, cut the fish's belly open starting from the anal vent and slicing forward.
Pull out the guts.
Now, use the heel of the knife (the end of the blade closer to the handle, as opposed to the tip of the knife) to sever the spine, and now, the head should come off.
In the opened stomach cavity (up near the spine) there is some bloody tissue, so make a slit with the knife as shown and wash it out thoroughly under running water.
If you use a bamboo cleaning brush or a toothbrush, you can get the inside of the fish really clean. After washing, wipe the fish dry, and clean off your chopping board.
Next, cutting from the fish's back, you'll feel a sort of gritty sensation as you slice along the spine to divide the fish into three pieces. Don't rush this step. It's important to keep the angle of the knife blade even as you cut.
With katsuo and other soft-fleshed fish, you almost don't even have to turn the fish over to finish filleting it...although, it is a little tricky.
OK, we've managed to fillet the fish. What's left is to remove the fatty waste tissue and the bones that are in the middle of the fish. You can also remove the skin as needed.
And now the question is: how to serve your fish?
I recommend slicing it into sashimi and eating it with some grated ginger and grated garlic. Or, chopped up and seasoned with ponzu sauce is also an excellent choice!!
Story Behind this Recipe
Katsuo are in season.
The flesh of this fish is very soft, so when you prepare it, avoid ragged, sloppy cuts by always keeping the angle of your knife the same. Freshness is vital! Immediately cook any leftovers in another dish. In Step 13, I wrote that you can cut the fish without flipping it over, but if it's too difficult, go ahead and turn the fish over to cut. Don't worry! It takes lots of practice to be able to do anything new.