Start with sushi-grade fish from a reliable source

The fish you use for sushi must be sushi-grade, which means it has been frozen to a temperature that kills parasites — typically −4°F (−20°C) or colder for seven days, or −31°F (−35°C) for fifteen hours. This is not a grade assigned by the government; it is a standard that reputable fishmongers follow. When you buy from a fish counter, ask directly: "Is this sushi-grade?" A honest fishmonger will tell you yes or no. If they hesitate or say "it's fresh," that is not the same thing.

The fish most reliable for home sushi are salmon, tuna (especially ahi or yellowfin), and sea bass. Buy the thickest, most uniform piece you can find — at least one and a half inches thick — because you will be slicing it, and thin pieces fall apart. Ask the fishmonger to cut it from the center of the fillet, not the tail end. If you are buying frozen sushi-grade fish, thaw it in the refrigerator for six to eight hours, never at room temperature.

Key Takeaways

  • Sushi-grade fish has been frozen to kill parasites; ask your fishmonger directly whether the fish meets this standard before you buy.
  • Thaw frozen sushi-grade fish in the refrigerator for six to eight hours, and keep it cold until the moment you slice it.
  • A sharp knife, a cutting board reserved for raw fish, and a single clean stroke matter more than speed — hesitation and sawing motion bruise the flesh.
  • Slice against the grain at a shallow angle to create pieces that are tender to bite and visually clean.
  • Prepare your fish no more than two hours before serving, and keep it on ice until you build your rolls or nigiri.

Chill everything before you start

Temperature control is the difference between sushi that tastes clean and sushi that tastes off. Place your cutting board in the freezer for fifteen minutes before you begin. Put the fish on ice — a shallow bowl filled with ice, with the fish on a plate set on top — and keep it there until you are ready to slice. If your kitchen is warm, work quickly and return the fish to ice between cuts.

Wet your knife blade with cold water before each slice. This prevents the fish from sticking to the blade and tearing. Keep a bowl of ice water next to your cutting board and dip the knife between every cut or two. This small step changes how the fish looks and feels in your mouth.

Use the right knife and technique

A sashimi knife or a very sharp chef's knife at least eight inches long is essential. The blade must be sharp enough that you can slice a tomato with no pressure — if you have to push, the knife is too dull and will crush the fish instead of cutting it. Dull knives are the most common mistake home cooks make.

Hold the knife at a shallow angle — about thirty degrees from the cutting board — and use one smooth, single stroke from the heel of the blade to the tip. Do not saw back and forth. Do not hesitate mid-slice. One motion, one clean cut. This matters because each time the blade tears the flesh instead of cutting it cleanly, you expose more surface area to air and bacteria, and the texture suffers immediately.

Slice against the grain of the fish — the direction the muscle fibers run. For most fish, this means slicing perpendicular to the length of the fillet. Slicing against the grain makes each piece tender to bite. If you slice with the grain, the pieces will be stringy and harder to chew.

Portion and thickness for different preparations

For nigiri (fish over rice), slice the fish into pieces about one-quarter inch thick and roughly two inches long by one inch wide. These pieces should drape slightly over the rice without overpowering it.

For rolls, slice the fish into strips about one-quarter inch thick and three to four inches long, depending on how wide you want your roll. The strips should be uniform so they cook evenly in the roll and look neat when you slice the finished roll.

For sashimi (fish alone), slice thicker — about one-half inch — and cut larger pieces, three inches long by one and a half inches wide. Thicker pieces are more forgiving and show off the texture and flavor of good fish.

Keep your workspace clean and separate

Use a cutting board reserved only for raw fish. Do not use the same board you use for vegetables or cooked food. Wash the board with hot soapy water and dry it completely before you start. If you are preparing multiple types of fish, slice the milder fish first (like white fish or sea bass) and the stronger fish last (like salmon or tuna), so flavors do not transfer.

Wash your hands before you begin and after handling raw fish. If you touch your face, your phone, or anything else, wash your hands again. These are not dramatic precautions — they are the baseline of working safely with raw food.

Store sliced fish on ice until service

Once you have sliced the fish, arrange it on a plate set over a bowl of ice. Cover it loosely with plastic wrap or a damp paper towel so it does not dry out. Do not let the plastic touch the fish directly, or it will stick. Keep the fish on ice and use it within two hours of slicing.

If you are preparing sushi for guests and need to slice the fish ahead, slice it no more than one hour before serving. The longer raw fish sits, even on ice, the more the texture changes and the more the flavor fades. Fresh is not just better — it is the whole point.

Common mistakes and how to avoid them

The most common mistake is using a dull knife. A dull blade crushes the fish and makes it look gray and bruised instead of translucent and bright. Sharpen your knife before you start, or have it professionally sharpened if you have not done so in months.

The second mistake is slicing too thick or too thin. Too thin and the fish falls apart or looks ragged. Too thick and it is hard to bite and does not feel right in your mouth. Practice with one piece until you find the thickness that feels right for the dish you are making.

The third mistake is letting the fish warm up. Every minute the fish sits at room temperature, the texture changes and bacteria multiply. Work quickly, keep everything cold, and return the fish to ice the moment you are done slicing.

Frequently Asked Questions

Can I use regular grocery store salmon for sushi?

Only if the fishmonger tells you it is sushi-grade and has been frozen to the proper temperature. Most grocery store salmon is not frozen to the parasite-killing standard, even if it looks fresh. Ask directly before you buy. If they cannot confirm it is sushi-grade, do not use it for raw preparations.

What if I do not have a sashimi knife?

A very sharp chef's knife at least eight inches long works well. The key is sharpness, not the knife's name. A dull sashimi knife is worse than a sharp chef's knife. If your knife is not sharp enough to slice a tomato with no pressure, sharpen it or have it sharpened before you begin.

How long can I keep sliced sushi fish in the refrigerator?

Use it within two hours of slicing. After that, the texture changes, flavors fade, and the risk of bacterial growth increases. If you need to prepare fish ahead, keep it whole and on ice, then slice it just before you build your rolls or plates.

Is it safe to prepare sushi at home?

Yes, if you start with sushi-grade fish from a reliable source and keep everything cold. Sushi-grade fish has already been frozen to kill parasites. The main risk is bacterial growth, which you prevent by keeping the fish on ice and using it quickly. Work cleanly, keep your tools and board separate from other foods, and you will be safe.

What is the difference between sashimi and nigiri?

Sashimi is fish alone, sliced and served without rice. Nigiri is a small mound of rice topped with a slice of fish. Both use the same preparation — sushi-grade fish, sharp knife, clean slices — but nigiri pieces are usually thinner and smaller because they sit on top of rice.