Splendid alfonsino: 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.
• Kinmedai (splendid alfonsino): up to once a week (about 80 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

• The provisional regulatory limit (total mercury 0.4 ppm) does not apply to deep-sea fish and shellfish. The kinmedai average (0.654) exceeds the limit, but the fish is outside the limit and has a guidance amount for pregnant women instead. We found no official document explaining the reason for the exemption.
• The methylmercury in one serving (about 80 g) of kinmedai (average 0.535 ppm) is about 43 μg. That is about 39% 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).
• In the MAFF survey (fiscal 2007–2010, 120 samples), average total mercury was 0.77 ppm (median 0.70) and methylmercury 0.65 ppm (median 0.58), close to or slightly higher than the MHLW compilation (0.654, 0.535). The maximum total mercury was 2.8 ppm, so there is individual variation.
• The yardstick for “how much is OK” differs by agency: the tolerable weekly intake is 2.0 μg/kg body weight for the FSCJ, 1.6 for JECFA, and 1.3 for EFSA. The guidance amounts were built on the FSCJ’s 2.0. → How much fish is OK during pregnancy?
• The concentrations by fish species are from a compilation through fiscal 2008 (May 2010), and the national guidance table has not been revised since June 2010. The MHLW 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.

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)”
• MAFF, “Provisional Regulatory Limits for Mercury in Fish and Shellfish”
• FSCJ, Evaluation of the tolerable weekly intake of methylmercury (August 2005), document posted by the MHLW
• 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
• Swordfish and striped marlin
• Whales and dolphins
• Salmon
• Mackerel
• Sardines, horse mackerel, and Pacific saury