If you don’t have newspaper, you can also use butcher paper. Or, if you are outdoors, you may just need to use whatever surface you have available and remember to rinse down your workstation well afterwards.
Work in an area that is large enough for you to easily flip the fish over when you need to.
If your tuna is already headless, then you can skip making this initial cut.
Be careful to not hurt your hand on any of the spiny fins.
Use a strong, sharp filleting knife so you can cut the fish as easily as possible. Avoid making a sawing motion with your knife, as that could tear up the meat of the fish.
You could cut off the entire tail of the fish, though you don’t have to. Leaving it intact gives you an additional place to hold the fish while you’re cutting and flipping it.
As you are cutting the fish, keep in mind that you will be separating its body into 4 nearly equal quarters—2 from the belly and 2 from the top.
You may need to also cut from the middle of the fish to fully detach the quarter from the tuna, depending on its size.
You may also need to cut from the belly to fully detach the top loin, depending on how large your fish is.
When you’re done, you will have 4 quarters of tuna and a carcass, consisting of the head, spine, and tail.
If you’re out on a boat, have a bucket to put your fish carcass into and discard of it once you’re docked again. Don’t throw it back into the water, as it can attract birds or other wildlife.
The bloodline of a tuna has a very strong flavor and will change the taste of the meat in an unpleasant way, so you want to remove it. If you don’t do it right away when you are filleting the tuna, remember to remove it later before you cook it. Discard both the belly fat and the bloodline.
If you prefer, you can actually skin the top 2 quarters of the fish by simply pulling it off with your hands. Grab a corner of the skin and pull it backwards, peeling it off. This technique won’t work for the bottom belly quarters, though, as the meat there is more delicate and will rip more easily.
Be sure to pick up the fish quarters and rinse both sides of them.
If your tuna quarters are too big, you can cut them in half or into quarters before storing them. If you don’t have butcher paper, you can wrap them in plastic wrap, or even put them into resealable bags.
If any fish liquids got into crevices on your counter, use a toothbrush, soap, and hot water to scrub those areas.
If you are out camping or fishing, bring along an ice-box filled with ice to store your fish in. Label your fish with the date it was filleted so you remember how long it will be good for.
