Swordfish and striped marlin: mercury

Levels measured in Japanese government surveys and studies

Units are mg/kg (= ppm). Values are for the edible portion of fish on the market and appear to be wet weight (the sources do not say). Total mercury and methylmercury were not necessarily measured in the same samples. The MAFF rows (fiscal 2007–2010) give the median next to the mean.

How much to eat (official advice)

• The guidance applies to “women who are pregnant or may become pregnant” (MHLW, revised June 2010). Children, women who are breastfeeding, and adults other than pregnant women are not covered.
• Swordfish (mekajiki): up to once a week (about 80 g/week).
• Striped marlin (makajiki): up to twice a week (about 160 g/week).
• One serving is calculated as about 80 g (one serving of sashimi, or one slice of fish). One piece of sushi or sashimi is about 15 g.
• If you eat two kinds of “up to once a week” fish in the same week, halve the amount of each. If you eat one “up to once a week” fish and one “up to twice a week” fish in the same week, also halve the amount of each.
• Even if you eat too much in one week, eating at one meal or over one week does not greatly change the mercury level in your body, and it is explained that you can simply eat less the following week.

Limits (Japan, international, EU)

Good to know

• Fish concentrations are about the same in Japan and the US; the advice differs. For swordfish, average total mercury is 1.003 ppm (51 samples) in the Japanese compilation and 0.995 ppm (636 samples) in the US survey. Japan says “up to once a week (about 80 g)” and the US says “avoid.” We have not found documents from either country explaining why they differ. → How Japan’s standards differ from other countries’
• The methylmercury in one serving (about 80 g) is about 57 μg for swordfish (average 0.712 ppm) and about 30 μg for striped marlin (0.372 ppm). That is about 51% and 27% of the FSCJ’s tolerable weekly intake (2.0 μg/kg body weight per week; 111 μg per week for a 55.5 kg person) (Urayomi’s calculation).
• How the guidance amounts are built is public. From the tolerable weekly intake, the mercury coming from foods other than fish and from fish and shellfish outside the table is subtracted (what can be allotted to the covered fish is 78.94 μg per week), and the remainder is divided by each fish’s average methylmercury. For swordfish, 78.94 ÷ 0.712 = about 111 g per week, so it went into the table as a fish of which three 80 g servings a week (240 g) cannot be eaten.
• The provisional regulatory limit (total mercury 0.4 ppm) does not apply to tuna, billfish (kajiki), skipjack, and similar fish. The swordfish average (1.003) exceeds the limit, but the fish is outside the limit and has guidance amounts instead.
• In the MAFF survey (fiscal 2007–2010, 120 samples), swordfish averaged 1.3 ppm total mercury with a maximum of 3.9 ppm, higher than the MHLW compilation (1.003). The national guidance table has not been revised since June 2010.
• The MHLW is not asking pregnant women to avoid fish; it calls on people to avoid eating large amounts of fish high in mercury in a lopsided way, so as to keep the benefits of eating fish. Cadmium is low in muscle: swordfish was 0.03 (maximum 0.04, 5 samples) in the MAFF survey.

Related explainers

• How Much Fish Is OK During Pregnancy? Guidance for Tuna, Canned Tuna, and Kinmedai, with Mercury Numbers
• Why Do Heavy Metal Standards Differ Between Japan and Other Countries? Japanese, Codex, and EU Standards and Tolerable Intakes Compared

Pages for each metal

• Mercury

Sources

• MHLW, “Notes on Eating Fish and Shellfish and Mercury for Pregnant Women” (revised June 2010)
• MHLW, “Notes on Eating Fish and Shellfish and Mercury for Pregnant Women,” Q&A
• MHLW, Document 2-4, “Survey Results on Mercury in Fish and Shellfish (Summary)” (May 2010)
• MAFF, “Data Collection of Survey Results on Hazardous Chemicals in Food (Fiscal 2003–2010)”
• FSCJ, Evaluation of the tolerable weekly intake of methylmercury (August 2005), document posted by the MHLW
• US FDA/EPA, “Advice about Eating Fish” (October 2021)
• US FDA, “Mercury Levels in Commercial Fish and Shellfish (1990-2012)”
• European Commission, Regulation (EU) 2022/617 (maximum levels for mercury in food)

Last checked 2026.10.03 (against the original government documents and papers, collected and cross-checked in Gemini Notebook).

Also in “Fish”

• Pacific bluefin tuna and southern bluefin tuna
• Bigeye tuna
• Yellowfin tuna, albacore, and young Pacific bluefin
• Canned tuna
• Skipjack tuna
• Splendid alfonsino
• Whales and dolphins
• Salmon
• Mackerel
• Sardines, horse mackerel, and Pacific saury