Introduction
Quick answer: Buy fish from a seller who can explain how it should be served. Keep it cold, use a clean board and knife, pat the surface dry, remove pin bones, and cut only what you will use. Raw preparation cannot make unsafe fish safe.
- Separate raw fish from cooked food.
- Wash hands before and after handling it.
- Choose a cooked recipe if the source is uncertain.
Learning how to prepare fish for sushi is one of the most important skills for anyone who wants to make better nigiri, sashimi, and sushi rolls at home.
Learning how to prepare fish for sushi correctly makes every later step, from slicing sashimi to shaping nigiri, much easier.
Many beginners focus on the final slicing step, but professional sushi preparation begins much earlier.
Before a piece of fish becomes beautiful sashimi or nigiri, it usually needs to be inspected, trimmed, cleaned, divided into manageable sections, and shaped into blocks that are easier to slice consistently.
In professional sushi kitchens, these rectangular pieces are often referred to as saku blocks.
A properly prepared saku block makes the next step much easier because the fish has already been shaped with its grain, thickness, and intended use in mind.
During my years working with sushi, I learned that good fish preparation is not about cutting away as much as possible.
It is about understanding which parts should be kept, which parts should be trimmed, and how the shape of the fish affects the final slice.
If you’re still deciding what type of seafood to work with, start with my guide to the best fish for sushi.
Once you have properly sourced fish, this guide will show you how I approach preparing it for sushi.
What Is a Saku Block?
A saku block is a clean, manageable piece of fish prepared for slicing into sushi or sashimi.
Instead of trying to cut individual sashimi slices directly from a large irregular fillet, sushi chefs first shape the fish into sections that are easier to control.
A good saku block usually has:
- A clean surface
- An even thickness
- A manageable width
- No remaining bones
- Little unnecessary connective tissue
- A shape that allows consistent slicing
The exact size depends on the fish and how it will be used.
There is no single perfect measurement that works for every species.
Tuna, salmon, yellowtail, sea bream, and other fish all have different body structures.
The goal is not to force every fish into exactly the same rectangle.
The goal is to create a practical shape that allows clean slicing.
Start With Properly Sourced Fish
Good knife work cannot fix poor-quality fish.
Before beginning any preparation, make sure the seafood is appropriate for the way you intend to use it.
If you plan to eat the fish raw, buy from a reputable supplier and ask specifically whether the product has been handled for raw consumption.
The term “sushi-grade” by itself should not be your only standard.
Look at the fish carefully.
Fresh fish should generally have firm flesh and a clean, mild aroma rather than a strong fishy or ammonia-like smell.
The FDA’s guide to selecting and serving seafood safely also recommends keeping seafood properly refrigerated and preventing cross-contamination during preparation.
When working with raw seafood, sourcing and handling are just as important as knife technique.
Keep the Fish Cold While You Work
Before you start trimming, prepare your cutting board, knife, paper towels, containers, and other tools.
Don’t take the fish out first and then begin searching for equipment.
Keep the fish refrigerated until your workstation is ready.
The FDA recommends storing seafood at 40°F (4°C) or below when refrigerated.
When I prepare fish, I try to work efficiently and return unused portions to refrigeration as soon as possible.
This doesn’t mean rushing.
It means having an organized workstation so the fish does not sit at room temperature unnecessarily.
Inspect the Fillet Before Cutting
Before making the first cut, take a moment to study the fish.
This is a habit that becomes increasingly important as your knife skills improve.
Look at:
- The thickness
- The direction of the muscle
- The belly section
- The back section
- Any remaining bones
- Skin or silver skin
- Dark bloodline
- Thin or uneven edges
Don’t immediately start cutting simply because the fish is on the board.
First decide what you want each section to become.
Some pieces may work well for nigiri.
Others may be better for sashimi.
Smaller or irregular pieces may be useful for rolls, spicy fish mixtures, or other preparations.
Planning before cutting reduces waste.
Remove Remaining Bones Carefully
Depending on how the fish was processed, you may still find rib bones or pin bones.
Run your fingers gently over the flesh to locate anything that remains.
The objective is to remove bones without unnecessarily damaging the surrounding meat.
If you’re trimming around rib bones, keep the knife close to the bones.
The farther the knife moves away from the bone, the more usable fish you lose.
This is one of those techniques that improves with practice.
Beginners sometimes try to make one large aggressive cut.
I prefer controlled cuts.
Follow the structure of the fish.
Let the bones guide the knife.
Trim the Belly and Uneven Edges
After removing bones, look at the shape of the remaining fillet.
You may see thin belly sections, rough edges, connective tissue, or pieces that won’t produce good sushi slices.
Trim these areas carefully.
But don’t automatically throw them away.
One of the habits professional cooks develop is finding the best use for every usable part of the fish.
A thin section that doesn’t work well for beautiful sashimi may still be excellent in a roll.
Smaller pieces can sometimes be used for chopped preparations.
The best-looking center portions can then be reserved for nigiri or sashimi.
Good fish preparation is partly about matching each section to the right purpose.
Understand the Different Sections of the Fish
A large fillet doesn’t have exactly the same texture from end to end.
The thickness, fat content, and grain can change depending on the section.
This is why I don’t treat the entire fillet as one uniform piece.
Back Section
The back section is often relatively firm and consistent.
Depending on the fish, it can produce excellent slices for sashimi or nigiri.
Belly Section
The belly may contain more fat and can have a softer, richer texture.
With fatty fish, this can be one of the most desirable portions.
Tail Section
The tail becomes thinner and often requires a different cutting strategy.
It may be more practical for rolls or smaller preparations depending on the fish.
Learning to recognize these differences helps you decide how to divide the fillet.
Remove the Skin With a Controlled Cut
If the fish still has skin and your preparation requires skin removal, position the fillet securely on the cutting board.
Start at an end where you can create enough skin to hold.
Then keep the blade relatively flat as you separate the flesh from the skin.
You don’t need excessive force.
A sharp knife and controlled movement are more important.
Try to keep the knife close to the skin so you leave as much usable flesh as possible.
The exact technique will vary depending on the fish because some skins are thicker or more firmly attached than others.
After removing the skin, inspect the surface.
There may still be thin connective tissue or areas that need additional trimming.
Don’t Over-Trim the Fish
One common mistake is trying to make the fish look perfect too early.
Beginners sometimes keep cutting until every edge looks completely square.
That can create unnecessary waste.
Remember that you’re eventually going to slice the fish again.
A small irregularity that doesn’t interfere with your final slices does not always need to be removed.
I prefer to trim with a purpose.
Ask yourself:
Will this section interfere with the finished sushi?
If the answer is no, you may not need to remove it.
Professional fish preparation is not about creating perfect geometric shapes.
It is about producing useful, clean portions efficiently.
Divide the Fillet Into Manageable Sections
Once the bones, skin, and unnecessary tissue have been addressed, you can begin dividing the fillet.
This is the point where the large piece starts becoming recognizable sushi blocks.
Look at the thickness of the fish.
If one section is much thicker than another, separating them can make slicing easier later.
Keep the intended final product in mind.
For example, a block prepared for nigiri may be shaped differently from a piece intended for thin sashimi slices.
The most important factor is control.
A huge fillet is harder to slice precisely.
A well-proportioned block is easier to hold, position, and cut consistently.
This is an important part of learning how to prepare fish for sushi because the shape of the block determines how easily it can be sliced later.
How to Shape a Saku Block
Now begin shaping the sections into clean blocks.
When learning how to prepare fish for sushi, creating a clean and manageable saku block is one of the most useful skills to practice.
You are looking for a piece that sits securely on the cutting board and provides enough depth for your intended slices.
I usually pay attention to three things.
Width
The block should be wide enough to produce a properly sized piece of sashimi or nigiri topping.
Height
If the block is extremely thin, creating attractive angled slices becomes more difficult.
Grain Direction
Pay attention to the structure of the muscle.
Your final slicing direction will affect tenderness and appearance.
This is why saku preparation and final slicing technique are closely connected.
After your blocks are ready, my guide on how to slice fish for sushi explains how cutting angle, thickness, and knife movement affect nigiri and sashimi.
Why Saku Blocks Make Sushi Easier
There is a practical reason professional sushi kitchens prepare fish in manageable blocks.
Consistency.
Imagine trying to cut ten identical nigiri toppings from a large irregular fillet.
Every cut would require a slightly different angle.
Now imagine working from a clean, even block.
Your hand position stays more consistent.
Your knife angle becomes easier to repeat.
Your slices become more uniform.
This is particularly helpful when you’re still developing your knife skills.
Good preparation makes the final technique easier.
Example: Preparing Salmon for Sushi
Salmon is a good example because its muscle lines are easy to see.
After removing the necessary bones and skin, look at the direction of the white fat lines running through the flesh.
Instead of immediately cutting the fish into small pieces, first decide which direction will give you attractive final slices.
Divide the salmon into practical blocks.
Keep the surface clean and avoid crushing the flesh with your fingers.
Salmon is relatively soft compared with some leaner fish, so unnecessary pressure can affect the appearance.
When the block is shaped correctly, the natural fat lines can create beautiful patterns in your nigiri and sashimi.
This is one reason salmon is a useful fish for beginners practicing sushi preparation.
Salmon is also an excellent fish for practicing how to prepare fish for sushi because its grain and fat lines are easy to see.
How I Decide Which Pieces Become Nigiri
When I break down a fish, I don’t expect every piece to become nigiri.
For nigiri, I prefer sections that allow me to make consistent slices with a clean shape.
I look for:
- Suitable thickness
- Attractive grain
- Clean texture
- Enough width for an angled slice
- Minimal connective tissue
Irregular pieces aren’t necessarily bad pieces.
They simply may have a better use.
This mindset greatly reduces waste.
Instead of asking, “Is this piece perfect?”
Ask:
“What is the best use for this piece?”
That is a much more practical way to think like a professional cook.
How I Decide Which Pieces Become Sashimi
Sashimi puts the fish itself at the center of the plate.
Because there is no rice underneath the slice, shape and texture become especially noticeable.
For sashimi, I generally want clean sections that allow smooth, attractive slices.
The thickness will depend on the fish.
Some fish are enjoyable with a firmer, thicker cut.
Others are better with thinner slices.
There is no reason to force every species into exactly the same presentation.
Understanding the fish is more important than memorizing one measurement.
Use Smaller Pieces for Rolls
Trimmings and smaller clean sections can be extremely useful for sushi rolls.
For example, pieces that are too narrow for ideal nigiri may still be perfect for:
- Tuna rolls
- Salmon rolls
- Yellowtail rolls
- Spicy fish preparations
- Hand rolls
This is another reason I avoid excessive trimming.
The goal isn’t simply to produce beautiful saku blocks.
The goal is to use the fish intelligently.
Good restaurants pay attention to yield because seafood is valuable.
Home cooks should develop the same habit.
Keep Your Knife Clean
As you work, moisture, fat, and small pieces of tissue can accumulate on the blade.
Wipe the knife when necessary with a clean damp towel.
A clean blade gives you better control.
It also helps prevent the knife from dragging across the surface of the fish.
Use smooth movements rather than sawing back and forth.
If you find yourself using excessive pressure, check your knife.
A sharp knife should do most of the work.
Keep the Cutting Board Organized
Fish preparation can become messy very quickly if you allow every trimming and finished block to remain on the board.
I like to separate the workstation into areas.
One section for the fish I’m currently cutting.
One container for usable trimmings.
One area or tray for finished blocks.
Waste goes somewhere else.
This makes it easier to see what you’re doing and helps prevent finished pieces from becoming mixed with scraps.
The same principle applies to the entire sushi process.
An organized workstation improves both speed and consistency.
Food Safety Matters During Fish Preparation
Raw seafood requires careful handling.
Wash your hands before and after handling raw fish.
Keep knives, boards, dishes, and work surfaces clean.
Avoid transferring raw seafood juices to vegetables, cooked foods, or other ready-to-eat ingredients.
The FDA recommends washing cutting boards, dishes, utensils, and countertops between raw seafood preparation and ready-to-eat food preparation. You can review the complete FDA seafood safety recommendations here.
Also remember that freezing requirements for fish intended to be eaten raw can depend on the species and how the fish was raised or handled.
The FDA Food Code contains specific parasite-destruction requirements and exceptions for applicable fish.
For home sushi, buying from a trusted supplier who understands raw consumption is much better than assuming any supermarket fish can be eaten raw.
What to Do After Your Saku Blocks Are Ready
Once the fish has been shaped, keep it cold until you’re ready for final slicing.
Don’t leave all your prepared blocks sitting on the cutting board while you make rice, prepare vegetables, or organize plates.
Do those jobs beforehand whenever possible.
Keep the surface of the fish clean and protected.
When you’re ready to make sushi, remove only the amount you need.
Then move to your final slicing step.
For nigiri and sashimi, this is where knife angle and thickness become especially important.
For rolls, the block may be cut into longer strips instead.
Pair Properly Prepared Fish With Good Sushi Rice
Fish preparation is only half of great sushi.
The other major component is the rice.
Beautifully prepared fish on poorly seasoned rice still won’t create restaurant-quality sushi.
Your rice should be glossy, tender, slightly sticky, and properly seasoned.
If you’re still improving your rice technique, use my complete guide to making perfect sushi rice at home.
When the rice and fish are both prepared correctly, sushi becomes much easier to assemble.
Common Mistakes When Preparing Fish for Sushi
Understanding these mistakes will help you learn how to prepare fish for sushi with less waste and more consistent results.
Cutting Before Studying the Fish
Look at the shape, thickness, and grain before making your first major cut.
Removing Too Much Meat With the Bones
Keep the knife close to the bone structure.
Over-Trimming
Don’t throw away good fish just to create a perfectly rectangular block.
Ignoring Grain Direction
Think about how the block will eventually be sliced.
Leaving the Fish Out Too Long
Prepare your workstation first and return unused fish to refrigeration.
Using a Dull Knife
A dull blade can crush or tear delicate fish.
Treating Every Part of the Fish the Same
Different sections may be better suited for nigiri, sashimi, or rolls.
Throwing Away Usable Trimmings
Clean smaller pieces can often be used in rolls or other preparations.
Professional Tips From a Sushi Chef
One of the most important things I learned is to slow down before making the first cut.
Once a piece of fish has been cut away, you can’t put it back.
Look at the entire fillet first.
Decide where your best blocks are likely to come from.
Think about what you plan to make.
Nigiri?
Sashimi?
Rolls?
Using the final dish to guide your breakdown makes the process much more efficient.
Another important habit is consistency.
When you find a shape that works well for your knife and your preferred sushi style, try to reproduce it.
Over time, preparing saku blocks becomes much faster because you begin recognizing useful shapes immediately.
Frequently Asked Questions
What is a saku block?
A saku block is a clean section of fish shaped into a manageable piece for slicing into nigiri or sashimi.
Do I need to make perfectly rectangular blocks?
No.
The goal is consistency and easy slicing, not perfect geometry.
Different fish naturally produce different shapes.
Should I remove all the skin?
That depends on the fish and the preparation.
Some sushi preparations use skin or specially treated skin, while others require it to be removed.
Can I use the smaller trimmings?
Yes.
Clean usable trimmings can often be used for sushi rolls, hand rolls, or chopped preparations.
Is preparing fish the same as slicing sashimi?
No.
Preparing the fish creates the clean block.
Final slicing turns that prepared block into sashimi or nigiri toppings.
Can I use any supermarket fish for raw sushi?
Don’t assume that any fresh-looking fish is appropriate for raw consumption.
Purchase from a trusted supplier and specifically ask about its suitability and handling for raw use.
Why does my fish tear when I cut it?
Common causes include a dull knife, a dirty blade, using a sawing motion, or applying too much pressure.
Final Thoughts
Learning how to prepare fish for sushi gives you much more control over the final result.
A professional-looking piece of nigiri doesn’t begin when you cut the final slice.
It begins when you inspect the fillet.
You remove the bones carefully.
You understand the different sections.
You trim only what needs to be trimmed.
You shape the fish into manageable blocks.
Then you choose the best use for each piece.
During my years working with sushi, I’ve learned that this preparation stage is where a great deal of quality is either protected or lost.
Take your time.
Use a sharp knife.
Keep the fish cold.
Keep your workstation clean.
And remember that every part of the fish does not need to become the same thing.
Once your saku blocks are ready, continue with my guide on how to slice fish for sushi.
If you’re still choosing ingredients, see my guide to the best fish for sushi, and complete your foundation with perfect sushi rice.
Master these fundamentals and making clean, consistent sushi at home becomes much easier.