The white fish that occupy most of your supermarket's showcase are pleasant, non-assertive and mostly interchangeable. That's not the case with mackerel. This darker, richer fish -- filled with heart-healthy omega-3 fatty acids -- has a bold, distinctive flavor of its own. Like other high-fat fish, mackerel is best when impeccably fresh, either caught yourself or purchased when just landed. This often means cleaning and filleting them yourself, but mackerel are easy to handle.
Mackerel are striking fish, with a skin that's beautifully mottled in silver, black and slate-grey. When they're at their freshest, they smell just faintly of the sea, and their eyes are clear and rounded, and if you press a finger against the mackerel's side, you won't leave an indentation. Don't be alarmed if the fish is strangely rigid. That's just rigor mortis, and it's a sure-fire sign your mackerel is fresh. Like most fish, it's best after rigor has come and gone. Just put the mackerel on ice or into a cooler, and refrigerate them as soon as you get home.
Mackerel have a thin skin and tiny scales, so they're one of the few fish that don't need their scales removed before you clean or fillet them. Cleaning a mackerel is quick and simple, even if you rarely work with whole fish. You'll need a filleting knife or utility knife with a long, thin, sharp blade.
Place the mackerel on a cutting board. Cut off the head, or -- if you prefer to leave the head on -- cut the throat from gill to gill.
Hold the mackerel's back in your hand, and rotate the fish until you see the tiny opening that marks its sphincter. Insert the tip of your knife there, just deeply enough to penetrate the skin.
Slide the knife tip the length of the mackerel's belly until you reach the cut at its throat.
Reach in with a finger and scoop out the fish's entrails, then rinse the belly cavity with cold water.
Wear a good pair of disposable kitchen gloves while working with the mackerel. Gloves provide a better grip than bare fingers and keep your hands from smelling of fish, and make the whole process a bit less cringe-worthy for squeamish cooks.
If you prefer to eat your mackerel in the form of boneless fillets, you have a few more steps to complete. This is easiest if you've left the head on during cleaning, because it provides a convenient grip for your hand. If you already know how to fillet any other common fish, the process will be very familiar.
Hold the mackerel firmly by the head and slide the knife blade underneath the bony gill plate -- toward the head -- until it meets the backbone.
Turn your knife so it rests horizontally on the backbone, pointing toward the tail. Draw the knife in long, even strokes from the head to the tail, lifting the fillet away from the bones but leaving it attached at the tail.
Flip the fish to its other side and repeat the process.
Cut the two fillets from the tail. leaving behind the head, tail and skeleton. Holding the knife at a very flat angle, cut away the ribs and their connecting membrane from each fillet.
If you want skinless fillets, skin them before cutting them away from the tail. Use the tail as your grip and slide your knife through the flesh at the narrow end of the fillet until it reaches the skin. Pull back gently on the skin and push forward gently with your knife, until the fillet comes away completely from the skin.
Some cooks prefer to remove the strong-tasting "blood line" of dark flesh that runs the length of the mackerel near the backbone. Make a narrow, shallow V-shaped cut on either side of the bloodline, then grip it with your fingertips. It should pull right out, though you might have to encourage it a little with your knife.
One-Step Cleaning and Filleting
Fish-plant workers turn whole mackerel into boneless fillets in a single step, reducing the entire cleaning and filleting process to two skilled sweeps of the knife. This method takes a bit of practice and results in slightly smaller fillets, but it's remarkably efficient. It takes a bit of effort to explain the technique in words, but you'll understand it immediately when you see it done by an expert.
Feel the mackerel's belly with your fingertips, noting where the relatively firm muscle gives way to the softer belly cavity.
Grasp the whole fish by its head, and cut downwards at the neck until your knife blade reaches the spine.
Draw the blade toward the tail in a smooth, sweeping stroke, angling it around the belly so it leaves the ribs behind and doesn't cut into the belly cavity.
Flip the fish and repeat the process, cutting away the second fillet. Skin the fillets and remove the blood line, if you wish.
If you cut too deeply and get a portion of the ribs or belly cavity in your fillet, just trim it away carefully with your knife once you're done.