Why Raw Fish Deserves Your Full Attention

There is something deeply satisfying about slicing a piece of fish you have prepared yourself, laying it over warm vinegared rice and eating it within seconds. But raw fish is one of the most demanding ingredients in any kitchen. Unlike cooked food, it never passes through a heat stage that would destroy parasites or bacteria, so everything depends on how it was caught, transported, stored and handled before it reaches your board.

In the UK, two hazards matter most. The first is parasites, particularly Anisakis larvae, which are found in wild sea fish and can cause serious gastric illness if swallowed alive. The second is bacterial growth: fish spoils fast, and the cold chain from boat to shop to fridge must never break. Histamine is a third concern, a toxin that builds up in certain oily fish such as mackerel and herring if they are not chilled almost immediately after landing. It is not destroyed by cooking or freezing. Good news: all three risks are manageable with a few firm habits.

Sourcing: Ask the Right Questions

Forget the phrase "sushi grade". It has no legal definition in the UK and tells you nothing. What you actually need to know is how the fish has been handled and whether it has been frozen to parasite-killing temperatures. A good fishmonger will answer these questions happily, and if they look baffled, buy your fish elsewhere.

Look for shops with high turnover, ideally ones that deal with restaurants. Ask when the fish arrived and whether it has been commercially frozen. Much of the salmon sold in Britain has been frozen at sea, which is good news for you. Inspect whole fish where you can: bright, clear eyes, pink-red gills, a fresh sea smell, and flesh that springs back when pressed. Fillets should look glossy and moist, not dry at the edges or sitting in cloudy liquid. Buy at the end of your shop, take a cool bag, and get it home into the fridge straight away.

The Freezer Is Your Safety Net

Official guidance in the UK and across the EU is that fish intended to be eaten raw should be frozen at -20°C or colder for at least 24 hours, or at -35°C for 15 hours. This kills parasites but does nothing for bacteria, so it is only one part of the picture.

Here is the catch. Most domestic freezers sit at around -18°C, which does not meet that standard. Check yours with a fridge thermometer and look for a fast-freeze function. If your freezer cannot reach -20°C, you have two sensible options: buy fish that was commercially frozen before you bought it, or accept a longer freeze. Many home cooks freeze at -18°C for 48 to 72 hours as a practical compromise, but be clear that this is a compromise, not a guarantee.

• Freeze fish on the day you buy it, not three days later.
• Wrap it tightly or vacuum seal it, and freeze it flat so it chills quickly.
• Thaw it slowly in the fridge, on a rack over a plate, for 24 hours.
• Never thaw fish on the counter or in warm water.

Keep Everything Cold and Clean

Work in short bursts and keep the fish in the fridge between steps. Aim for the fish to spend no more than two hours out of the cold in total. A bowl of ice under your board helps on warm days.

Use a dedicated board and knife for raw fish, or wash them in hot soapy water and dry them thoroughly before and after. Wash your hands often, especially after handling fish and before touching rice or garnishes. Keep raw fish away from salad, fruit and anything eaten uncooked. Salt, citrus juice, soy sauce, wasabi and alcohol do not kill bacteria or parasites, so never treat a marinade as a safety step. If you are making several rolls, keep finished pieces covered in the fridge and bring them out just before serving.

Which Fish to Choose and Which to Leave

Farmed fish is generally the safer choice for home sushi because controlled diets reduce parasite exposure. Excellent options include farmed salmon, farmed sea bass, farmed sea bream and farmed yellowtail. Tuna loin is popular but demands real freshness, as histamine risk rises quickly.

• Avoid all freshwater fish raw, including trout from rivers and lakes, carp and tilapia. Their parasite risks are different and harder to eliminate.
• Be cautious with wild mackerel, herring and sardines unless you know they were chilled within minutes of landing.
• Skip raw shellfish at home unless it comes from a reputable, licensed supplier with full traceability. Vibrio and norovirus are real concerns.
• Pregnant women, young children, older people and anyone with a weakened immune system should avoid raw fish entirely.

Serving, Leftovers and Knowing When to Stop

Raw fish is at its best within 24 hours of thawing or buying, and it should never be refrozen. Once you have made your sushi, eat it the same day. Do not save leftover raw fish or assembled rolls for tomorrow, however good your fridge is. If fish smells sharp, feels sticky, or has dulled in colour, throw it out without hesitation. The cost of a piece of fish is nothing next to a week of illness.

Cooked fillings, pickles and vegetables are far more forgiving, so if you are feeding a crowd or cooking with children, build your spread around those and keep the raw fish for a small, well-chilled, well-timed treat. Practise the cold chain, the freezer routine and the clean board, and making sushi at home becomes the relaxed, joyful thing it should be.