Fish

Completeness scorecard

Deterministic gap audit — no score is composite, no cell is LLM-judged. Each chip is re-derivable by re-running tools/evidence/build-ingredient-scorecard.mjs. review: residuals and missing data are worked autonomously via data/evidence/ingredient-scorecard-review-flags.csv and wiki/completeness-gaps.md.

Fish is the dominant dietary source of methylmercury exposure for most populations (EPA Fish Advice).

Heavy metal contamination profile

Per-analyte snapshot derived from the machine-readable contamination_profile in the frontmatter above. data gap indicates the literature has been reviewed for this commodity-analyte combination and no usable occurrence data was found (a finding, not a placeholder). The Key sources column shows the top 2-3 contributing sources by year and sample size, with numbered wikilink aliases.

Why this commodity accumulates heavy metals

Fish accumulate methylmercury through aquatic-food-web biomagnification: inorganic mercury in water is methylated by sulfate-reducing bacteria in sediment, taken up by plankton, and biomagnified through each trophic step. Predator species at the top of marine food webs (swordfish, shark, king mackerel, tilefish, bigeye tuna, marlin) carry methylmercury concentrations 1 to 2 orders of magnitude above small-pelagic species (sardines, anchovies, herring) and farmed or short-lived freshwater species (salmon, tilapia, trout). See mercury for the methylmercury toxicology, the JECFA 61st PTWI of 1.6 µg/kg b.w./week, and the Faroe Islands and Seychelles cohort literature on developmental neurotoxicity (synthesized in mercury).

Cadmium and lead in fish are commodity-secondary concerns; bivalve molluscs (covered separately at bivalve-molluscs) are the dominant marine-food Cd source (EFSA Cd 2009).

Multi-metal coverage and dedicated subpages

Fish-as-a-commodity is broad enough that future ingest waves will likely produce species-specific pages (tuna, salmon, swordfish) rather than a single fish page treating all species uniformly. The current page is a placeholder that satisfies the wikilink graph and orients consumers toward the dominant concern (methylmercury).

Collado-Lopez et al. 2025 reports fish/fish-mix baby foods as a priority review-level group for arsenic and mercury, with median As 0.165 mg/kg and median Hg 0.016 mg/kg among detected items. This signal should guide retrieval of the underlying primary studies before any fish-containing baby-food p90 is calculated. collado-lopez2025-heavy-metals-baby-food-formula

Regulatory limits that apply

• jecfa-methylmercury-ptwi — JECFA provisional tolerable weekly intake of 1.6 µg methylmercury/kg b.w./week.
• efsa-methylmercury-twi — EFSA tolerable weekly intake of 1.3 µg methylmercury/kg b.w./week.
• EPA Fish Advice — FDA/EPA joint advice for women who might become pregnant, women who are pregnant or breastfeeding, and young children.
• eu2023-contaminants-maximum-levels and eu-2023-915-cadmium — EU fish maximum levels are species- and tissue-specific. General muscle meat of fish is 0.30 mg/kg (300 ug/kg) Pb, 0.050 mg/kg (50 ug/kg) Cd, and 0.50 mg/kg (500 ug/kg) Hg; listed lower-mercury fish are 0.30 mg/kg (300 ug/kg) Hg, and listed higher-mercury fish including tuna, shark, swordfish, marlin, halibut, pike, and sturgeon are 1.0 mg/kg (1000 ug/kg) Hg.

Sources

Auto-generated from source-page frontmatter. The “Used on this page for” column is populated by the orchestrator’s POPULATE-SOURCE-LEGEND action; pending entries appear as *[awaiting synthesis]*.

Ranges by source, region, and variety

The dominant axis of variance in fish heavy-metal load is trophic position. Methylmercury biomagnification is multiplicative through each trophic step: small filter-feeders and herbivorous fish carry low Hg; mid-level predators carry moderate Hg; apex predators carry the highest Hg. Within a given species, individual variance is large and is driven by body size (older, larger individuals carry higher Hg because exposure accumulates over a lifetime), trophic specialization (an individual that feeds higher in the food web than average for its species will carry higher Hg), and waterbody history.

Marine versus freshwater origin is the secondary axis. Marine apex predators (shark, swordfish, king mackerel from the Gulf of Mexico, bigeye tuna, marlin, tilefish from the Gulf) routinely test in the high-Hg range; the FDA “Avoid” tier in the FDA/EPA fish-consumption advisory is built around these species. Freshwater wild fish from waterbodies near historic mining, chlor-alkali industry, or coal-fired power generation can carry Hg comparable to marine apex predators despite lower trophic position, because watershed Hg loading is locally elevated. Farmed freshwater fish (catfish, tilapia, farmed salmon) typically carry the lowest Hg because feed-mediated exposure is lower and lifespan is shorter than wild equivalents. See freshwater-fish for the freshwater-specific synthesis.

Geographic variance is documented at the waterbody level. The Great Lakes carry an active fish-consumption advisory program because of legacy Hg + PCB loading. The Gulf of Mexico carries tilefish-specific advisories. Subsistence-fishing populations in the Arctic and in parts of the Amazon basin carry the highest documented chronic MeHg exposures globally because of cultural reliance on apex predators and marine mammals.

Cadmium in fin-fish is generally low because cadmium is not significantly biomagnified through the aquatic food web in the way mercury is; the dominant marine-food Cd source is bivalve molluscs (bivalve-molluscs, EFSA Cd 2009). Lead in fish is similarly low except where waterbody loading is elevated. Total arsenic in fin-fish is dominated by arsenobetaine and is not health-equivalent to inorganic arsenic; see arsenic-total for the speciation interpretation rule.

Processing effects

Methylmercury is bound to cysteine residues in fish muscle protein and is not reduced by ordinary cooking, smoking, or canning. Cooking can slightly concentrate Hg per gram of finished product through water loss, but the total methylmercury per serving is approximately conserved. Removing the skin reduces lipophilic contaminants (PCBs, dioxins) but does not reduce methylmercury, because methylmercury is in the muscle tissue itself. Removing the dark muscle (where present) can slightly reduce per-serving methylmercury in some species, but is not a routine consumer practice.

Canning concentrates fish solids relative to fresh form (water loss, sometimes oil or sauce added). The methylmercury load per can of tuna or sardines reflects the source-fish methylmercury level adjusted for canning yield. Smoking does not reduce methylmercury; some smoking processes can add trace metals from smoke or curing salts, but this is small relative to the underlying matrix load. Surimi (paste from low-trophic fish, used in imitation crab and similar products) carries lower Hg than the species mix would suggest because surimi is made from short-lived species deliberately.

For cadmium and lead in fish, where the matrix carries low baseline loads, processing effects are similarly small relative to source variability. The dominant determinant of finished-product metal load is still the species and sourcing decision, not the processing decision.

Ingredient-derivative risk

Fish oil supplements (omega-3, EPA/DHA, cod liver oil) are a separate exposure pathway with distinct contamination patterns. Methylmercury is concentrated in muscle protein and is largely partitioned out of the oil fraction during pressing and refining; commercial fish oil typically carries lower MeHg than the source fish on a mass basis. However, the lipophilic contaminants (PCBs, dioxins) that the oil fraction does carry are concentrated in fish oil, and reputable manufacturers run molecular distillation to reduce these to acceptable levels. Cod liver oil specifically can carry higher cadmium and lead than refined fish oil because the liver is the storage organ for some metals. See dietary-supplements (Cat 16 supplement oil-based) for the supplement-specific routing.

Fish flour and fish protein concentrate, used as feed additives and in some fortification applications, can concentrate metals where they were present in the source fish. Fish sauce, where fish are fermented in salt for extended periods, carries metal concentrations broadly proportional to the source fish but with variability driven by fermentation length and salt source. Imitation surimi-based products carry the surimi base’s lower Hg.

Mitigation options

For fish, mitigation operates almost entirely at the sourcing and consumption-pattern levels. Unlike rice or cocoa, where agronomic and processing levers can substantially shift the finished-product metal load, fish methylmercury is determined by the species and waterbody at the point of catch and cannot be reduced through downstream processing.

Sourcing levers are the dominant intervention. Choosing low-trophic, short-lived species (sardines, anchovies, herring, salmon, tilapia, catfish) over apex predators (shark, swordfish, king mackerel, tilefish, bigeye tuna) reduces methylmercury exposure by one to two orders of magnitude. Farmed-fish sourcing typically reduces Hg below comparable wild-caught species. Geographic provenance matters: avoiding waterbodies with active fish-consumption advisories is the operational rule. See supply-chain-screening for the sourcing-screening framework.

Consumption-pattern levers apply at the consumer level. The FDA/EPA joint fish-consumption advisory categorizes fish into three tiers (best choice, good choice, avoid) and recommends weekly serving counts calibrated by tier. Pregnant women, women of childbearing age, breastfeeding mothers, and young children are the priority audiences. Substituting two best-choice servings per week for one avoid-tier serving reduces methylmercury exposure substantially without losing the cardiovascular and neurodevelopmental benefits of fish in the diet.

Testing and QC levers are routine in brand QA. Lot-level methylmercury testing on incoming fish, particularly for high-Hg species and value-added products targeting infants and pregnancy populations, is standard practice in regulated supply chains. See testing-and-qc for sampling-plan and method considerations; icp-ms for the analytical method.

Processing levers are limited for methylmercury. Removing dark muscle and skin marginally reduces methylmercury in some species but does not change the order-of-magnitude exposure picture. For commercial preparation of low-Hg-target fish products, the dominant intervention is source-species selection upstream.

Packaging and storage levers are not consequential for methylmercury in fish; the metal is bound to muscle protein and does not migrate to packaging materials in a way that affects finished-product Hg load. Canned fish carries the standard tinplate-migration Sn consideration (packaging-and-storage).

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.