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  • Writer's pictureKiwi Blade Knives

Choosing a filleting knife: What's right for you?

Updated: May 10, 2019

Outdoor boat fishing and fish filleting

It’s been a great day’s fishing and you’re looking at your quota of fish. You’re about to start the ‘fun’ job of filleting but you hate your knife, what do you do?

If you are like a lot of people you will just grab whatever is at hand and carry on regardless but having a good knife can make all the difference to how you feel about filleting as well as to what those fillets are going to look like later in your pan – and on your plate; tatty shreds or shiny fresh fillets that are a credit to your day – and your fishing prowess.

It’s not just about the knife keeping a sharp edge, although that is important.

The comfort of the handle, the flexibility and the length and width of the blade all matter - not to mention the weight of the entire knife and the type of steel that the blade is made from.

Size matters

Depending on what kind of fish you catch most often, your filleting knife should match.

In general, a 6 to 9 inch (150mm – 230mm) blade will be more than ample for most table fish.

Beyond that, for big fish such as a yellowfin tuna, which weigh in in the region of 40 – 50kgs, you obviously need something more substantial such as a 12 inch blade (300mm). Big game fish require an extremely rigid 15 inch (380mm) blade or longer.

And the small fish? They should be swimming freely in the water again.

Flex but don’t bounce

For me, personally, the biggest focus is ‘will the blade go where I steer it?’ A filleting knife has to have a bit of flex but still be reasonably rigid. Anything more than a 5cm flex on a 30cm blade will see your blade bouncing off bones and shearing into flesh that might not be what you intended to cut – and that includes your fingers. A flimsy uncontrollable knife, as well as a blunt knife, is a danger to your physical health – fingers are useful for more than just catching fish!

Blade width is a bit of a contentious issue here too. If you use a typical Western style filleting knife the thickness of your knife spine will probably be between 1.5mm to 2.5mm and the blade width will be not more than an inch wide (25mm). A slightly wider blade is often used for the skinning of the fish, whereas a thinner blade is used for the actual filleting and cutting into the fish.

If you are more drawn towards the Japanese style of filleting you will probably be using a much wider and heavier knife. The Japanese have made filleting, alongside other forms of knife use, into an art form. It’s not uncommon to see a skilled Japanese filleter using a 7mm spine Deba knife which has a width of 50mm or wider. Check out a video demonstration here

Sharp and to the point

In terms of wear resistance, (how quickly your knife will lose its sharpness) … I know this is a real bugbear for a lot of fishermen and fisherwomen.

All blades will lose their sharpness over time – just as all blades need to be washed and oiled after every use in order for them not to rust in the long term – but some blades will definitely lose their sharpness sooner than others. No surprises, it depends on the quality of the steel that the knife is made from.

Stainless steel is a good kind of steel to have in this environment. It comes in many compositions and there are trade offs – some go blunt sooner but are softer and easier to sharpen yourself while others keep a sharp edge but are difficult to sharpen ‘on the fly’ as they need very good ceramic or diamond stones to sharpen them. It all depends on what works best for you. If you are wanting more specialised help in this regard, you can always contact me here

In general though, a good quality stainless steel blade with more than 1% carbon in it, should do the trick. The knife you buy should indicate the percentage of quality steel it has in it. Stainless steel is a wide and varying steel type and traditionally, can have a mix of multiple steels – from chrome to molybdenum to tungsten, cobalt and more. It’s a subject that I like to go down the wormhole into quite often but the joys of metallurgy are a bit beyond the scope of this article.

Too blunt too soon?

You should be able to fillet at least 20 average sized fish without needing to sharpen your knife – and when you do sharpen it, you should sharpen it on a ceramic rod or Japanese water stone. The ceramic rod is for quick maintenance ‘on the fly’ while you are still filleting - and one or two strokes each side of the blade should get the edge of your blade back to where you want it.

After that, you will want to sharpen your knife more carefully with a Japanese water stone.

If you feel your knife is losing its ability to cut after about 50 – 60 pan-sized fish, it is probably time for a water stone sharpening session.

For yellowfin tuna and larger fish with heavier bones and tougher skins, you should be able to fillet at least one big fish (over 30kg) before you feel the need to sharpen your knife again.

I sharpen on Japanese water stones ranging from 200 grit up to 10,000 grit but for most people a range from 1000 grit to around 6,000 grit should be sufficient.

Rust never sleeps – much like dolphins (kind of)

While dolphins do actually have the ability to sleep with at least one half of their brain, not unlike some people I know … let’s just say that no knife is impervious to the tendency to rust but stainless steel blades are your best choice for being corrosive resistant.

Don’t put them in the dish washer, don’t leave them laying around in water or damp conditions and always wash, oil them with a good vegetable oil, and dry them after use and they should last you for a very long time. The same goes for both salt water environments as well as fresh water fishing.

Consider your environment

If you are using your knife onboard a boat, you may also want to secure your knife so that you don’t lose it overboard. Attaching some buoyant foam rubber tubing to your handle and securing it to a cord can help, as can buying a knife with a Day-Glo handle in case you need to find your knife in the dark. It is all personal preference.

Many people choose not to take their knives onboard boats and use them only when back on terra firma (for the very reason that they don’t want to lose them or have them exposed, unnecessarily, to the elements).

Getting a sheath or pouch to carry your knife in is also a great idea – just don’t leave your knife in there unwashed – especially if the sheath is made of leather and the humidity is high. Your knife will rust in no time at all.

If you need to go all day, comfort is everything

As tough as we all are, there is nothing fun about filleting for hours with an uncomfortable or unnecessarily heavy knife.

A lightweight but strong filleting knife is the answer.

A filleting handle should fit well in the palm of your hand. It should be shaped or slightly ridged so that it doesn’t twist or slip unexpectedly in your wet hands. Scalloped and shaped handles that fit to the form of your hand - as well as rough surfaced wooden handles - are a good choice here.

Phenolic resins such as G10 and micarta and materials such as kirinite are also good to use as they are extremely hygienic and fluid resistant.

Your handle should have no sharp edges on it and it should also have a definite stopping point or bolster at the top end of it so that your fingers know to ‘go no further forward’ toward the blade.

Buying a knife that can also be used as a sashimi knife is an additional double bonus – and is one feature you might want to look out for when considering what kind of knife to buy. What could be better than fish straight from the catch onto a board with wasabi and soy sauce? Life doesn’t get much better!

In an ideal world, however, you should have a knife for each job – filleting, skinning and cutting sashimi. How far you stretch the demands of your knife will depend on your budget.

A knife is not a fancy bottle opener – treat it with respect

At the end of the day, we all have different needs. Taking time to consider yours before buying will stand you in good stead for finding a knife that works for you, both now and in the long term.

A truly good filleting knife is more than ‘just a knife’. It’s most definitely not a bottle opener, it’s not a can opener or a wood chopper, or something to dig out the rust of your aunty’s car with – as tempting as those ideas might be. It is a tool, purpose built for the job.

If accorded the care it deserves, your knife will be impressing both you and your guests with fat sumptuous piscine fillets for years to come.

Happy fishing!

Willie van Niekerk is a knife maker who is based in Auckland, New Zealand

Willie van Niekerk displays a snapper at Puheke Beach
Fishing Heaven - Puheke Beach in Northland

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