In summary: AESAN table: small fish (anchovies, sardines, boquerones) have very low mercury (<0.05 mg/kg). Medium fish (bonito, skipjack tuna, cod) have low-medium mercury (0.05-0.5 mg/kg). Large predators (fresh bluefin tuna, swordfish, shark) have high levels (1-2 mg/kg) — avoid during pregnancy.
Table of contents
Legal limits and recommendations
EFSA (European Food Safety Authority) sets maximum mercury limits:
- General fish: 0.50 mg/kg
- Predators (tuna, swordfish, shark, pike): 1.00 mg/kg
Tolerable Weekly Intake (TWI): 1.3 μg/kg body weight. A 70kg adult = 91 μg/week.
AESAN recommends limiting high-mercury species during pregnancy, lactation, and for children <10 years old.
Mercury table by species (mg/kg fish)
| Fish | Mercury mg/kg | Category | Recommendation |
|---|---|---|---|
| Cantabrian Anchovy | 0.02-0.04 | VERY LOW | Unrestricted consumption |
| Fresh Boquerón | 0.03 | VERY LOW | Unrestricted consumption |
| Sardine | 0.02-0.05 | VERY LOW | Unrestricted consumption |
| Smoked Salmon | 0.03-0.08 | LOW | Unrestricted consumption |
| Cod | 0.08-0.15 | LOW | 2-3 servings/week |
| Octopus | 0.15-0.30 | MEDIUM | 1-2 servings/week |
| Canned Bonito del Norte | 0.15-0.30 | MEDIUM | 2-3 servings/week |
| Canned Skipjack Tuna | 0.20-0.40 | MEDIUM | 2 servings/week |
| Caviar | 0.05-0.10 | LOW | Unrestricted consumption |
| FRESH Bluefin Tuna | 1.00-2.00 | HIGH | AVOID during pregnancy |
| Swordfish | 1.20-2.50 | VERY HIGH | AVOID during pregnancy |
| Shark / Dogfish | 1.50-3.00 | VERY HIGH | AVOID during pregnancy |
| Pike | 1.20-2.00 | VERY HIGH | AVOID during pregnancy |
Why large fish accumulate more mercury
This is the bioaccumulation phenomenon: mercury in ocean waters concentrates as it moves up the food chain. Plankton → small fish → medium fish → large predatory fish. Each level multiplies the concentration by 5-10x.
That's why anchovies (which eat plankton) have 0.03 mg/kg, while large bluefin tuna (which eat anchovies and other fish) accumulate 1-2 mg/kg over their 10-20 year lifespan.
How much can I consume depending on the situation
Healthy adult: no restrictions for fish <0.5 mg/kg. Limit fresh bluefin tuna/swordfish to <100g/week.
Pregnant / lactating: TOTALLY avoid bluefin tuna, swordfish, shark, pike. Fish <0.3 mg/kg = no restriction (anchovies, sardines, salmon, cod, octopus, canned bonito).
Children <10 years old: same restrictions as pregnant women. Prioritize anchovies, sardines, salmon, canned bonito.
Frequently asked questions
Do anchovies have mercury?
Is canned tuna dangerously high in mercury?
Octopus and mercury?
Does cod have a lot of mercury?
Is there a difference in mercury between fresh and canned fish?
Mercury in caviar?
In conclusion
Fear of mercury in fish affects the consumption of fish that are CARDIOPROTECTIVE and safe. If you understand the table: small fish (anchovies, sardines, boquerones) are a nutritional investment without risk. Large predatory fish (fresh bluefin tuna, swordfish) are the problematic ones. Cantabrian anchovies and sardines are the safest and most nutritionally dense options.
