Nutrition and daily life

Fish and seafood: safe choices

Fish is rich in protein, omega-3 fats and vitamin D and can be a good choice during treatment. But raw and undercooked fish, and some smoked and salted products, are risky when immunity is weak. This topic explains how to choose fresh fish, store it, cook it, and which products are best avoided for now.

Last updated: 7 October 2026~5 min read

On a dark navy background, a baked white fish fillet on a plate with opaque flakes separated by a fork, a lemon wedge beside it and light steam. — **Figure 1.**Cooked fish is opaque and flakes easily with a fork.

01Short answer

Well-cooked fish and seafood are valuable food during treatment. Fresh fish has bright eyes, firm flesh and a mild smell. Keep it in the fridge for 1–2 days or freeze it, and thaw it in the fridge. Cook fish until it is opaque and flakes with a fork (about 63 °C); prawns and squid until pearly white; mussels and oysters until their shells open — throw away any that stay closed. During neutropenia, sushi, sashimi, ceviche, raw oysters, raw or lightly salted fish (such as pickled herring), refrigerated cold-smoked fish, dried fish and unpasteurized caviar are usually not recommended. Canned fish, and smoked fish cooked in a hot dish, are safe.

02Simple explanation

Fish is a source of easily digested protein, omega-3 fats, vitamin D and iodine. When appetite is poor, gently cooked fish can be easy to eat.

Raw fish and shellfish can carry bacteria, viruses and parasites. Healthy people sometimes eat sushi without trouble, but during neutropenia the same food can cause a serious infection.

Oysters and mussels feed by filtering water and can collect germs. So they must always be fully cooked.

Listeria can grow even in the fridge. Cold-smoked fish (such as thinly sliced smoked salmon) is eaten without cooking, so it is risky when immunity is weak. Cooked in a hot dish, it is safe.

Canned fish (sardines, tuna, mackerel) is processed at high temperatures in the factory, so it is a safe and convenient choice.

03Scientific explanation

Cooking temperature: according to the FoodSafety.gov chart, finfish should be cooked to 63 °C (145 °F) or until the flesh is opaque and separates easily with a fork; shrimp, lobster, crab and scallops until pearly or white and opaque; clams, oysters and mussels until their shells open.

Weakened immunity: the CDC advises people with weakened immunity to avoid raw or undercooked seafood and refrigerated smoked fish, choosing instead smoked fish in sealed, shelf-stable packaging or cooked into dishes.

Choosing and storing: according to the FDA, fresh fish should smell fresh and mild, with clear, shiny eyes and firm flesh, and be sold on ice or in a refrigerated case. Do not buy shellfish with cracked or broken shells.

General health: the NHS recommends at least two portions of fish a week, one of them oily; large predatory fish such as shark, swordfish and marlin are best limited because they may contain mercury. A dietitian can build an individual eating plan.

04What happens in the body?

How to choose fresh fish

Bright, bulging eyes, red gills, flesh that springs back when pressed, and a fresh, mild smell. Fish should be on ice or in a chilled display. Frozen fish should have intact packaging without lots of ice crystals. Buy from a reliable place.

On a dark navy background, a whole fresh fish with clear, bright eyes resting on ice in soft cool light. — **Figure 3.**Fresh fish has bright eyes and firm flesh and is kept on ice.

Storing and thawing

Get fresh fish home quickly, keep it in a closed container in the coldest part of the fridge, and cook or freeze it within 1–2 days. Thaw it in the fridge, not at room temperature. Do not let raw fish juices drip onto other food; use a separate board.

Cooking: how to tell it is done

Fish: the flesh loses its translucency, turns white or pale and flakes easily with a fork. Prawns and squid: they turn from grey and translucent to pinkish-white and opaque. Mussels and oysters: the shells open as they cook — discard any that stay closed. You can bake, steam, stew or pan-fry.

What to avoid during neutropenia

Sushi and sashimi, ceviche, raw oysters, raw or lightly salted fish (pickled herring, home-cured fish), refrigerated cold-smoked fish, dried and salted fish, and unpasteurized caviar. All of these are eaten without cooking. Ask your team what becomes possible once your counts recover.

Safer choices

Baked or steamed fish, fish soup, fish cakes and fish balls (fully cooked inside), boiled prawns, fully cooked mussels, canned fish, and hot-smoked fish or smoked fish in a hot dish. Fish baked with vegetables or cooked in pilaf is a good choice too.

On a dark navy background, cooked pinkish-white prawns and opened mussels in a pot with rising steam. — **Figure 2.**Prawns are cooked until pinkish-white and mussels until their shells open.

Fish and medicines

Fish oil and omega-3 capsules can interact with some medicines and may increase bleeding risk when platelets are low. Talk to your team before taking any supplement. Cooked fish as food, on the other hand, usually causes no problems.

05Safe fish in four steps

Choose fresh, keep cold, cook through, avoid risky products.

1Choose freshBright eyes, mild smell.

2Keep cold1–2 days, or freeze.

3Cook throughOpaque, flakes easily.

4Avoid rawSushi, raw oysters, cold-smoked fish.

Protein and omega-3Easily digested food.

Lower riskCooking destroys germs.

An easy optionCanned fish works too.

06Fish and seafood during neutropenia (simplified)

Food	Riskier	Safer
Fish	Sushi, sashimi, ceviche	Fully baked, steamed or stewed
Salted and smoked	Pickled herring, cold-smoked salmon	Cooked in a hot dish, hot-smoked
Dried fish	Dried salted fish	Canned fish
Prawns, squid	Raw or half-cooked	Cooked until pinkish-white and opaque
Mussels, oysters	Raw oysters, shells that stay closed	Cooked until the shells open
Caviar	Unpasteurized	Check with your team

* The table is general information. After your counts recover or after a transplant, your team sets the rules.

07Key terms

Omega-3: Fatty acids from fish that benefit the heart and blood vessels.
Ceviche: A dish of fish “cooked” in lemon juice — in fact raw.
Cold smoking: Smoking at low temperature; the fish is not cooked.
Hot smoking: Smoking at high temperature; the fish is cooked.
Listeria: A dangerous bacterium that can grow in the fridge.
Mercury: A heavy metal that can build up in large predatory fish.
Shellfish: Seafood in shells, such as mussels and oysters.
Pasteurization: Gentle heating to kill germs.

08Key points

Cooked fish is a valuable source of protein.
Keep fresh fish 1–2 days or freeze it.
Cook fish until opaque.
Mussel shells must open; discard closed ones.
No sushi or raw oysters during neutropenia.
Eat cold-smoked fish in a hot dish.
Canned fish is a safe choice.
Check fish oil capsules with your doctor.

09Frequently asked questions

When can I eat sushi again?

It depends on your blood counts and treatment stage. After a transplant this can take a long time. Ask your team; in the meantime, rolls with cooked fish or vegetarian rolls are an option.

Does salted fish count as cooked?

No. Salt does not kill all germs. Lightly salted and home-cured fish is risky during neutropenia.

Can I eat black caviar?

Caviar is usually eaten without heat treatment. Unpasteurized caviar is not recommended during neutropenia. Talk to your team about pasteurized products.

Is frozen fish worse than fresh?

No. Properly frozen fish is nutritious and convenient. Thaw it in the fridge and cook it through.

Can I eat canned tuna every day?

Canned fish is safe, but variety matters. Tuna and other large fish can contain mercury, so it is better to alternate different fish. A dietitian can give individual advice.

Will fish oil help my immunity?

There is no evidence that omega-3 supplements strengthen immunity in leukemia, and in some cases they may increase bleeding risk. Talk to your team before taking them.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

When can I eat sushi again?
Does salted fish count as cooked?
Can I eat black caviar?
Is frozen fish worse than fresh?
Can I eat canned tuna every day?
Will fish oil help my immunity?

My questions

12Sources

U.S. Food and Drug Administration (FDA). Selecting and Serving Fresh and Frozen Seafood Safely
FoodSafety.gov (U.S. HHS). Cook to a Safe Minimum Internal Temperature
CDC. Safer Food Choices for People With Weakened Immune Systems
CDC. Preventing Listeria Infection
U.S. Food and Drug Administration (FDA). Food Safety for Older Adults and People with Cancer, Diabetes, HIV/AIDS, Organ Transplants, and Autoimmune Diseases
NHS. Fish and shellfish
NHS inform. Preparing and cooking food safely
American Cancer Society. Food Safety During Cancer Treatment
Memorial Sloan Kettering Cancer Center. Food Safety During Cancer Treatment
World Health Organization (WHO). Listeriosis — fact sheet
World Health Organization (WHO). Five keys to safer food manual
NHS. Food poisoning

Medical disclaimerThis information is for educational purposes only and does not replace medical advice.

Last updated: 7 October 2026← Back to the list

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