How to Fillet a Fish: The Cuts, and Why Two of Them Matter Twice

Five cuts, and nothing else

Filleting looks like butchery and is closer to tracing. Iowa’s Department of Natural Resources publishes the whole method in five steps, and the reassuring part is what it opens with: you do not need to remove the internal organs, head or fins, and the fillets are boneless.

The agency notes an accepted variation on step two: some anglers fillet the meat around the ribs rather than cutting through them. Slower, slightly cleaner, and a matter of preference rather than correctness.

Missouri’s Department of Conservation describes the same sequence in its own words — cut from behind the head down to the backbone, slide the knife with a sawing motion toward the tail, slice out the rib bones from top to bottom — and adds the skinning detail: cut down to the skin near the tail, turn the blade, pull firmly on the tail section, and saw the knife between the skin and the flesh.

The two tools that matter

Iowa’s DNR names a sharp fillet knife with a thin, flexible blade, and then a second item most people skip: a fillet glove on your free hand, to prevent serious cuts. That is the agency’s phrasing, not a manufacturer’s.

Missouri’s list adds a scaler — or a dull knife or a spoon — and a glove to protect your hand and help grip the fish, which is the underrated half of the job. The same page points out that many fishing accesses and parks provide cleaning stations with water for rinsing, and that a dock, a paddle, a cooler lid or a flat rock all work otherwise.

Flexibility is what the thin blade buys you. Steps three and four are both cases of the blade following a surface — skin in one, rib cage in the other — and a stiff blade cannot track a curve without leaving meat behind.

Why the skin and the dark strip come off twice over

Here is the part most filleting guides leave out, and it is the reason to do steps three and four properly rather than quickly.

Missouri’s Department of Conservation gives the taste reason: some fish, such as white bass and largemouth bass, have a strong-tasting dark layer of flesh along their lateral lines that should be cut away before cooking or storage.

The EPA, writing about fish advisories rather than cooking, gives a second one. Its factsheet states that lipophilic — fat-soluble — chemicals such as PCBs accumulate mainly in fatty tissues, and lists them:

belly flap, lateral line, subcutaneous and dorsal fat, dark muscle, gills, eye, brain, and internal organs

The agency’s conclusion follows directly: removal of internal organs and skin and trimming the fat before cooking will decrease exposure.

Read those two lists side by side. The dark strip Missouri tells you to cut for flavour sits exactly where the EPA says fat-soluble contaminants concentrate. The skin you remove for texture is on the same list. A careful fillet is doing two jobs at once, and neither requires you to believe anything about the other.

One honest limit belongs here. Trimming addresses fat-soluble contaminants. It does not address mercury, which binds to muscle protein rather than fat — which is why agency advisories treat the two separately and why trimming is never presented as a substitute for reading the advisory.

Species that need something extra

Not every fish comes apart the same way.

Catfish are scaleless, and Wisconsin’s DNR describes the skin as thick and tough. Its method is to make an incision around the head and down the belly, grip the skin with pliers, and pull it down toward the tail. Catfish can be filleted or cut into steaks. Our catfish fishing guide covers catching them; the agency also warns that the dorsal and pectoral spines are sharp and backed by venomous mucus glands, which is a cleaning-table concern as much as an unhooking one.

Large, older fish of any species deserve a second thought before the pan rather than a different knife. Wisconsin’s DNR explains the mechanism for walleye: they accumulate PCBs, pesticides and mercury in their bodies as they feed on smaller fish containing trace amounts of contaminants. For catfish the agency is more specific, noting that large individuals — generally those over 21 inches — from some waters may harbour high levels of pesticides or other toxins. This is one of the better arguments for catch and release on the biggest fish, alongside the fisheries one.

Panfish are often not filleted at all. Missouri’s alternative is pan-dressing: scale the fish by scraping the skin with a dull knife, spoon or scaling tool, cut along the sides of the fins on the back and behind the stomach and pull the fins out, remove the head, then slit the belly and scrape out the entrails. For a crappie or a bluegill that is often the faster route — see our panfish guide for which fish are worth which treatment.

Before you eat it

This is the one question a guide cannot answer for you. What is safe to eat, from which water, in what quantity, is published by your state agency as a fish consumption advisory — and Wisconsin’s DNR notes that it republishes its own every six months, listing the rivers and lakes whose fish are unsafe to eat.

Advisories are keyed to water body, species and often size, and they change. Look yours up before the fish goes in the cooler rather than after. Our licences and regulations guide explains where each state publishes them, along with the rules on how fillets must be transported and presented for identification, which also vary.