You can fillet a fish with any sharp knife. You cannot fillet one well. The difference is a thin, flexible blade that follows the backbone instead of cutting through it — and that is the single thing a filleting knife is built to do.

This guide covers blade length and flex, what edge type suits which fish, how to sharpen properly, and how to fillet safely on a bank where the ground is uneven and your hands are cold.

Why a filleting knife is different

A filleting knife has a thin blade — usually 1.2–2 mm at the spine — and almost no taper, so it can slide along a rib cage and over the backbone without levering through it. A general-purpose camp knife has a thick spine for batoning and prying, which is exactly the wrong shape inside a fish.

The thin blade also gives you feedback. You feel the spine of the fish through the blade, which is how you keep the cut shallow and leave the maximum amount of meat on the fillet.

Flex: the feature that matters most

Flex Behaviour Best for
Stiff Holds a straight line, less feel Cutting through rib bones, portioning, heavy fish
Medium Slight bend, good control General filleting, larger round fish
Flexible Bends along the backbone Flat fish, small fish, skinning fillets
Extra flexible Very thin, follows contours closely Delicate work, skinning, thin fillets

For most UK freshwater and inshore fishing, medium to flexible covers everything. A stiff blade is useful if you regularly cut through ribs on bigger fish; an extra-flexible blade is a specialist tool and frustrating on anything firm.

Blade length by fish size

  • 10–13 cm — small fish, trout, mackerel, pan fish. Precise and easy to control.
  • 15–18 cm — the all-round size for bass, pollack, carp and most UK sea and coarse fish.
  • 20–23 cm — larger cod, halibut and big carp, where one continuous cut along the backbone matters.

Longer is not better for small fish. An oversized blade on a mackerel gives you less control and more chance of cutting yourself, because your hand sits further from the work.

Plain, serrated or scalloped edge

A plain edge cuts cleanly through flesh and skin and can be resharpened for years. Serrated edges saw through scales and skin more easily but cannot be properly sharpened at home and leave a ragged fillet surface. Scalloped edges are a compromise that works on soft fish but struggles with firm flesh.

For a single knife, buy plain. Add a serrated knife only if you regularly deal with scaled, thick-skinned fish.

Close-up of a thin flexible filleting knife blade bending slightly, showing the narrow spine and sharp plain edge on a cutting board

Steel and handle materials

Stainless steel is the right choice for fishing: it tolerates salt water, blood and being rinsed in a lake. Carbon steel takes a keener edge but rusts unless you dry and oil it every single time — a deal-breaker on a bank.

Look for a handle that stays grippy when wet. Rubberised or textured synthetic handles beat smooth wood, which becomes slippery the moment it is covered in fish slime. A full tang — steel running the length of the handle — is stronger, but a well-made partial tang is fine on a thin fillet knife.

Sharpening without ruining it

  1. Use a fine stone or a ceramic rod, not a coarse grinder. Thin blades lose metal fast.
  2. Keep the original angle, usually 15–20 degrees per side. A filleting knife should be thinner than a camp knife.
  3. Sharpen little and often. Five strokes before each session beats a heavy regrind once a season.
  4. Never sharpen a flexible blade on a pull-through tool — it rounds the edge and removes too much metal.
  5. Dry and oil after use. Blood and water left on the blade is what causes pitting, even on stainless.
A filleting knife, sharpening stone and a protective glove laid out on a green bank mat beside a lake

Safe filleting on the bank

Most knife injuries in fishing happen in bad light, on soft ground, with cold hands. A few rules remove most of the risk:

  • Cut away from your body and keep the other hand behind the blade line, never in front of it.
  • Use a flat, stable surface. A board on a tackle box lid is better than a knee or a bucket.
  • Wear a cut-resistant glove on the holding hand if you are new to filleting.
  • Never cut towards a flexing blade — a thin knife can snap and travel further than you expect.
  • Keep the knife in a sheath between fish, not loose in a bag with hooks and lures.

Food hygiene matters too: the Food Standards Agency advice on clean surfaces and separate boards applies whether you are preparing fish at home or on a bank. Rinse the board, dry the blade, and keep raw fish away from anything you will eat without cooking.

What else you need on the bank

A filleting knife works with a proper landing net so the fish arrives in good condition, a mat to work on, and a container for fillets that keeps them cool. If you fish for predators, the pike lure guide covers handling and unhooking in more detail. Browse the fishing range for knives, boards and accessories.

FAQ

What is the best blade length for a filleting knife?

15–18 cm for most UK fishing. Go shorter for small fish and longer only for big cod or carp.

Flexible or stiff — which should I buy first?

Medium flex. It handles the widest range of fish and is the easiest to learn on.

Can I fillet with a normal kitchen knife?

You can, badly. A thick blade cannot follow the backbone and wastes meat. A dedicated filleting knife costs little and does the job properly.

Will stainless steel rust?

Less than carbon steel, but salt and blood will still pit it if you store it wet. Dry and oil it every time.

How do I carry a filleting knife legally?

Keep it in a sheath inside your kit, with a good reason to have it (fishing). Rules differ by country; check local law before travelling with any knife.

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