Fillet Knives 101

Fillet Knives 101

Posted by Captain Tom Migdalski on 28th May 2021

The right knife makes easy work of your catch.

As my father always coached me, “Use the right tool for the job.” That

axiom is never truer than with fillet knives. The greatest benefit of using a fillet

knife is the slender—and therefore maneuverable—blade, which can debone a fish

while minimizing flesh loss. The same applies to skinning fish: fish skin can be

either thin and delicate or thick and tough, and skinning a fish with a wide,

inflexible blade often leads to ripped skin or gouged and lost flesh.

Best Size and Use

Fillet knives, while they can be used for carving cooked meat like turkey or

roast beef, are not ideal for that purpose and are most useful for preparing raw

fish or removing breast meat from raw poultry or fowl. Fillet knives have a thin,

narrow, and flexible blade, which enables a skilled person to bend and maneuver the

knife around a fish vertebrae or bird breastbone to obtain the most meat possible.

(How to debone a chicken breast:

, how to fillet every type of fish:


Fillet blades are typically 6 to 9 inches long but can be as short as 4 inches.

Boning knives, the rugged cousin of fillet knives, are used to debone tough cuts of

meat or to disarticulate joints, such as separating chicken legs into parts or

removing a fish head or tail from its body. Those actions can quickly dull the sharp

edge of a fine fillet knife. Curved blades enable cooks to carve or precisely fillet a

piece of meat or fish, while wider (taller) and straighter blades provide quick,

simple, and straight slicing like carving proteins or chopping vegetables (like a

classic chef’s knife). In summary, stiff blades are good for tough cuts of meat

such as pork, beef, and venison, while flexible knives are preferred for dressing

raw poultry and raw fish.

“It’s all in the flex,” says lifelong saltwater angler and knife expert Elliott

Taylor. “The willingness of the blade to bend and follow the contour of the fish will

directly translate to the quality of your fillet and minimize wasted meat. Match

your knife to the fish you plan on filleting. You wouldn’t want to use the same blade

on a 25-pound striper as you would on a crappie. The larger the fish, the

larger—and usually somewhat stiffer—the fillet blade.”

A 4-inch blade is suitable for small fresh- and saltwater fish such as

panfish, trout, shad, porgies, winter flounder, or harbor bluefish. A 6-inch blade

also works well on small fish but gives you the versatility of handling medium-size

species like fluke, black sea bass, blackfish, and jumbo porgies. An all-purpose 7-

inch blade is a great choice for processing larger fish like adult bluefish, doormat

fluke, and medium striped bass. When you move up to large fish like tuna, shark,

cod, or large stripers, a 9-inch is best.

The Science of Steel

Steel is primarily a combination of iron and carbon. All steels contain other

elements in small, controlled amounts including manganese, sulfur, silicon, and

phosphorus. If no other elements are added, the steel is called carbon steel, which

is softer and easier to sharpen, but its drawback is that it rusts easily.

Steels used for rust-resistant blades are enhanced with additional minerals

called alloy steels. These give different types of steel special properties. Alloy

steels are made of iron, carbon, and other elements such as vanadium, nickel,

copper, boron, and chromium. When other elements comprising metals and non-

metals are added to carbon steel, alloy steel is formed.

These alloying elements are added to increase strength, ductility, hardness,

wear resistance, corrosion resistance, and toughness. The amounts

of alloying elements may vary between 1 and 50% and are labeled “stainless steel.”

These are most frequently used in making knives, scissor blades, surgical

instruments, and cookware.

Increasing carbon percentage increases hardness. Adding

chromium improves hardenability, wear resistance, and rust resistance. It’s a major

element in the popular culinary Martensitic stainless steels. Molybdenum and nickel

improve hardenability, tensile strength, and rust resistance, especially less pitting,

while vanadium increases hardenability and promotes desirable fine grains.

Some of the qualities of steel are defined this way:

 Hardness: Steel's ability to resist permanent deformation (measured on

the Rockwell Scale)

 Hardenability: Steel’s ability to be hardened through temperature


 Strength: Steel’s ability to resist applied forces

 Ductility: Steel's ability to flex or bend without snapping

 Toughness: Steel’s ability to absorb energy prior to breaking

 Initial Sharpness: Steel’s blade sharpness direct from the factory

 Edge Retention: Steel’s ability to hold a sharp edge

 Corrosion Resistance: Steel’s ability to resist environmental deterioration

 Wear Resistance: Steel’s ability to resist wear and abrasion

 Manufacturability: Steel’s ability to be easily machined, blanked, ground,

temperature-treated, and assembled

As steel is heated and cooled during manufacturing, its internal composition

changes. The structures formed during these changes are given names like

“Austenite” and “Martensite.” Martensite is a hard structure that’s created by

rapidly cooling steels after heat-treating. Metals that can form Martensite are

termed “Martensitic steels,” and it’s this steel that’s most useful in the cutlery

industry. Labels like S30V, BG-42, 154CM, 420HC, and 420J2 are all Martensitic

stainless steels. Each alloy recipe or type has exact specifications and is named

according to a number convention and have different price ranges. Martensitic

stainless steels, for example, have numbers like types 410, 420, and 425.

420J2, for instance, has a lower carbon content, and is a widely used,

general-purpose stainless steel. It offers fair hardness and corrosion resistance

and high ease of resharpening. It is ideally suited for knife blades with light to

medium use in routine applications at a reasonable price.

“Price here isn’t always as important as care,” says Taylor, “depending on

intended use. A $20 fillet knife with a synthetic handle that’s cleaned with soapy

water, hand-dried, and stored dry, will hold up better than a $140 blade with a

specialty handle that’s hastily thrashed in a bucket of water to get the blood off

and packed away wet, left in a salt environment, or run through a dishwasher. One

knife is best suited for the deck or marina cutting board while the other is best

for skilled food prep in a good kitchen.”

Japan and Germany have the reputation for making the best culinary knives.

Following them comes the USA. Knife metals from Taiwan are considered better

than steel from China, the latter of which is regarded as having the cheapest and

poorest quality blades.

Here’s a random sampling of fillet knives on the market, including point of

origin and approximate cost:

 Wüsthof Classic Fish Fillet Knife, 7-inch, exclusive high-carbon steel,

professional quality, Germany, $140

 Zwilling J.A. Henckels Pro Fillet Knife, 7-inch, 57 hardness on the Rockwell

Scale, Friodur ice-hardened, professional quality, Germany, $130

 Zwilling J.A. Henckels Twin Four Star II, 7-inch, stainless-steel,

professional quality, Germany, $120

 Shun Classic Flexible Fillet Knife, 7-inch, crafted of AUS8A, high-carbon

stainless steel, professional quality, hand-crafted in Japan, $100

 Shun Classic Boning and Fillet Knife, 6-inch, VG-MAX super-steel blade clad

on each side with 34 micro-thin layers of stainless steel creating a

Damascus-style blade, professional quality, handcrafted in Japan, $100

 AFTCO's 8", 10" and 12" fish fillet knives built in collaboration with Böker

Germany for premium blades featuring 4116 German stainless steel with full

tang construction and up-sweep design, commercial quality, 10-inch blade

$80, German steel assembled in Taiwan

 Cuda 7-inch semi-flex, wide, professional fillet knife, Titanium-bonded non-

stick, US 40A carpenter steel, $80, China

 Bubba Tapered Flex Fillet Fishing Knife, 7-inch, super-thin 8Cr13MoV Ti-

Nitride coated, rust resistant, $42, China

 Dexter-Russell Fillet Knife, 7-inch and 8-inch blades with plastic sheath,

high carbon, high alloy, stain free steel, commercial quality, $25, USA

 Cuda 6-inch fillet knife with sheath, 4116 stainless steel, $20, China

 Mercer Culinary Millennia Narrow Fillet Knife, 8.5-inch, one-piece, high-

carbon, stain-resistant, $12, Japanese steel, Taiwan

In summary, as with other products, you get what you pay for. A $100-$200

German or Japanese boning, fillet, or other food

prep knife is a superior cutting instrument in a well-appointed kitchen for people

interested and skilled in high-quality meal preparation. These knives should be

carefully honed, handwashed, hand dried, and stored in a knife block. To see and

handle such elite kitchen cutlery, stop in at Kitch, which is a

remarkably well-stocked kitchen, knife, and cookware store in the Olde Mistick

Village in Mystic, CT, and speak with owner and knife expert

Dan Price.

“However,” concludes Taylor, “if you’re just looking for a beat-around-the-

boat or back-at-the-dock fillet knife on a budget, a Dexter-Russell for under $30 will do a fine job when

properly handled and maintained.”