High mercury, high urea, and most shark fisheries are not sustainable.
Shark accumulates more mercury than almost any fish, and shark flesh contains urea that converts to ammonia unless treated. Many species are threatened.
Mercury accumulates up the food chain. Large, long-lived predator fish
eat many smaller fish and concentrate the methylmercury from every one of them, which is why
species size and lifespan predict mercury content better than anything
else.
Methylmercury crosses the placenta and affects foetal brain development, which is
why the advice for pregnancy is absolute rather than a matter of moderation.
Per 100g cooked.
Based on the nutrients and fibre this food supplies. These are supporting foods, not treatments.
Do not serve this to children or pregnant women. That is the whole
practical rule.
Occasional, not routine, for everyone
else.
Cook it to just done. These are lean, meaty fish that dry out
quickly.
Swap it for a low-mercury oily fish — salmon, trout,
sardine — if you want the omega-3 without the mercury.
Methylmercury binds tightly to protein in fish flesh, so it cannot be trimmed or
cooked away. Concentration rises with each step up the food chain, which is why a predator
that lives twenty years carries far more than a sardine that lives two.
Selenium in
fish appears to offer some protection against mercury toxicity, which complicates the picture
— but not enough to change the advice for pregnancy, where the developing brain is the
concern.
Shark flesh contains urea, which converts to ammonia. It must be
soaked or treated, and it smells strongly if not.
Pregnancy, trying to conceive, and young children: avoid entirely.
This is a high-mercury species and mercury crosses the placenta.
Everyone
else: occasional rather than routine.
Shellfish allergy is
separate from fish allergy.
This is information, not a prescription. If you are managing a diagnosed condition or taking medication, talk to your doctor before making a large change to your diet.
Nutrition figures on this page come from standard food composition data. These links let you check the numbers and read the underlying research yourself rather than taking our word for it.