Seatrout: a lean fish with a mercury limit

A meta-analysis of 18 to 21 randomized trials with 1392 to 1456 participants found that eating lean fish lowered blood triglycerides compared with eating no fish, with no significant change in total cholesterol or lipoproteins. The abstract does not give the size of that drop, and the trials covered lean fish as a class. We found no human study that names seatrout, so its health effects are inferred from fish in general. What is specific to seatrout is its mercury. FDA testing of 46 commercial weakfish samples, also sold as sea trout, found a mean of 0.235 ppm and single fish up to 0.744 ppm between 1991 and 2005, and local recreational catches can differ. FDA and EPA put weakfish and seatrout on the Good Choices list, which means one serving a week for people who are or may become pregnant, are breastfeeding, and for children. Per 100 g raw, USDA lists 16.74 g protein, 3 mcg vitamin B12 (125% of the Daily Value) and 36.5 mcg selenium (66%), from only two records.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• USDA lists raw seatrout at 16.74 g of protein, 3 mcg of vitamin B12 and 36.5 mcg of selenium per 3.5 oz (100 g), from just two records and no sample spread. — USDA FoodData Central SR Legacy record Fish, seatrout, mixed species, raw Evidence E source
  Per 100 g raw: protein 16.74 g (33% DV), vitamin B12 3 mcg (125% DV), selenium 36.5 mcg (66% DV); across the raw and cooked records B12 3 to 3.46 mcg, selenium 36.5 to 46.8 mcg, protein 16.74 to 21.46 g

What a real portion looks like

• FDA and EPA place weakfish/seatrout on the Good Choices list, which means one serving a week for people who are or may become pregnant, are breastfeeding, and for children. — People who might become or are pregnant or breastfeeding, and children aged 1 to 11 Evidence E source
  1 serving a week from Good Choices, versus 2 to 3 from Best Choices; a serving is 4 ounces for adults and about 1 to 4 ounces for children by age

What your body absorbs

• In an 8-week trial, cooked salmon raised blood EPA by 129% against 106% for cod liver oil, although the oil delivered 3.0 g of EPA and DHA a day versus 1.2 g from fish. — 71 volunteers in five groups: smoked salmon, cooked salmon, cooked cod, cod liver oil, control; 8 weeks (n = 71) Evidence C source
  Serum EPA +129% and DHA +45% with cooked salmon versus +106% and +25% with cod liver oil

What cooking and storage change

• Baking or frying lean finfish keeps about 90% of its vitamin B12 by the USDA retention table, while selenium, a main reason to eat seatrout, is not in that table at all. — USDA retention factors for the group Finfish and Shellfish Products, lean fish under 5% fat Evidence E source
  Vitamin B12 90% retained baked without drippings (Retn_Code 2301) and fried without coating (Retn_Code 2309); thiamin 90% baked, 85% fried; selenium and protein not covered by Release 6

What it does to your health

• A meta-analysis of 18 to 21 randomized trials with about 1,400 people found that eating lean fish lowered blood triglycerides compared with no fish, without a clear change in cholesterol. — Adults in crossover and parallel RCTs of lean fish or fish-derived protein, 1392 to 1456 participants (n = 1392-1456) Evidence A source
  Triglycerides lowered versus no fish (size not given in the abstract); no significant difference in total cholesterol or lipoproteins
• In a randomized trial of 95 adults with high blood lipids, 8.8 oz (250 g) of trout twice a week for 8 weeks cut LDL by about 23 mg/dL, while omega-3 capsules raised it by about 19. — Adults with hyperlipidemia in Shiraz, Iran; 47 fish and 48 capsule completers, 8 weeks (n = 95) Evidence B source
  LDL -22.75 +/- 27.28 mg/dL with fish versus +18.7 +/- 24.97 with 2 g/day omega-3 capsules, P < 0.001
• An umbrella review of 34 meta-analyses of cohort studies linked each extra 3.5 oz (100 g) of fish a day with 8% lower all-cause and 25% lower cardiovascular mortality. — Pooled prospective cohort studies, 298 primary cohorts Evidence C source
  All-cause mortality SRR 0.92 (95% CI 0.87 to 0.97); cardiovascular mortality SRR 0.75 (0.65 to 0.87) per 100 g/day

Safety, limits and interactions

• FDA testing of 46 weakfish (sea trout) samples found a mean of 0.235 ppm mercury, with single fish up to 0.744 ppm. — FDA monitoring samples of weakfish (sea trout), 1991-2005 (n = 46) Evidence E source
  Mercury mean 0.235 ppm, median 0.157, SD 0.216, min below detection, max 0.744

What people believe that the data does not support

• Neither the US 21 CFR health claims nor the EU claims register names seatrout or weakfish, so no seatrout-specific health claim is authorized. — 21 CFR 101 health claim sections and EU Register on nutrition and health claims, snapshot 2026-09-21 Evidence E source
  0 entries for seatrout, Cynoscion, weakfish, sea trout or fish consumption in either register

Who this works differently for

• In a meta-analysis of trials in children aged 2 to 14, eating fish raised blood vitamin D by about 4 nmol/L, a modest change, with no consistent effect on other micronutrients. — Children 2-14 years; vitamin D analysis 1,074 participants; seven studies, six of them RCTs (n = 1074) Evidence A source
  25(OH)D mean difference +4.08 nmol/L (95% CI 1.73 to 6.43); sensitivity +3.46 (1.03 to 5.65)
• A benefit-risk model put the methylmercury harm threshold at about 0.95 oz (27 g) of fish a day for fish averaging 0.23 ppm, close to the FDA mean for weakfish. — Model based on the nine most common fish in New Jersey markets and the EPA reference dose Evidence C source
  Harm threshold 27 g/day at 0.23 ppm MeHg versus 65 g/day at 0.1 ppm; benefit threshold about 15 g/day
• Pooled observational studies linked eating more fish with 21% lower depression risk, and 22% lower risk of depression in pregnancy. — 35 observational study articles, 44 studies; general and pregnant populations Evidence C source
  Depression RR 0.79 (95% CI 0.73 to 0.86); pregnancy-related depression RR 0.78 (0.69 to 0.89); significant only at 68.4 g/day or more

What is still unknown

• No human study in the corpus names seatrout or Cynoscion, so its health effects are inferred from fish in general, and no UK or survey portion data exist for it. — PubMed corpus snapshot pubmed:469432; CoFID 2021; FNDDS; USDA Foundation Foods Evidence E source
  0 corpus records for seatrout, Cynoscion, weakfish; no CoFID, FNDDS or Foundation entry; selenium absent from USDA retention table

The bottom line

The other trials used different fish. In a randomized open-label trial of 95 adults with high blood lipids in Iran, 8.8 oz (250 g) of farmed trout twice a week for 8 weeks lowered LDL by 22.75 mg/dL (SD 27.28), while 2 g a day of omega-3 capsules raised it by 18.7. Farmed trout is a fattier fish than seatrout. In children aged 2 to 14, a meta-analysis of seven studies, six of them randomized, found that eating fish raised blood vitamin D by 4.08 nmol/L (95% CI 1.73 to 6.43), and the authors note this may lack clinical relevance. In an 8-week trial without described random allocation, cooked salmon raised serum EPA by 129% against 106% for cod liver oil, although the oil supplied 3.0 g of EPA and DHA a day and the salmon 1.2 g. Cohort data are broader still. Each extra 3.5 oz (100 g) of fish a day was associated with 8% lower all-cause mortality (SRR 0.92, 0.87 to 0.97) and 25% lower cardiovascular mortality (SRR 0.75, 0.65 to 0.87), and fish tends to replace other foods and to track with income. Across 44 observational studies, 20 of them cross-sectional, more fish was associated with 21% lower depression risk (RR 0.79, 0.73 to 0.86), significant only from 68.4 g a day. By the USDA retention table, baking or frying lean fish keeps about 90% of its vitamin B12, a group factor from 1975. Selenium is not in that table, so we cannot say how much of it survives cooking. No US or EU health claim names seatrout or weakfish. The caution is mercury, and the official advice is written for pregnancy, breastfeeding and children aged 1 to 11. It counts a serving as 4 ounces for adults and about 1 to 4 ounces for children by age. A benefit-risk model put the harm threshold at about 0.95 oz (27 g) of fish a day for fish averaging 0.23 ppm methylmercury, close to the seatrout mean, using a reference dose that builds in uncertainty factors. In pregnancy, pooled observational data linked more fish with 22% lower risk of depression (RR 0.78, 0.69 to 0.89), an association that does not change the one-serving-a-week advice, which is set by mercury level.

Sources

1. stro-r4-01 · USDA FoodData Central, dataset
   Fish, seatrout, mixed species, raw (FDC 173695, SR Legacy, Finfish and Shellfish Products): protein 16.74 g per 100 g = 33% DV; vitamin B12 3 mcg = 125% DV; selenium 36.5 mcg = 66% DV; range over 2 records B12 3-3.46, selenium 36.5-46.8, protein 16.74-21.46; Foundation samples 0, CoFID match none
   USDA FoodData Central, SR Legacy, FDC 173695 · checked 2026-10-02
2. stro-r4-04 · FDA/EPA consumer advice
   Eat 2 to 3 servings a week from the 'Best Choices' list (OR 1 serving from the 'Good Choices' list).
   FDA and EPA, Advice about Eating Fish, 2024 · checked 2026-10-02
3. stro-r4-08 · controlled trial
   The serum content of EPA and DHA before and after intervention revealed a higher rise in EPA and DHA in the cooked salmon group (129% rise in EPA and 45% rise in DHA) as compared with CLO (106 and 25%, respectively) despite an intake of EPA and DHA in the CLO group of 3.0 g/d compared with 1.2 g/d in the cooked salmon group.
   Lipids, 2006 · checked 2026-10-02
4. stro-r4-02 · USDA Table of Nutrient Retention Factors, dataset
   USDA-RETN-R6:2301 FINFISH,<5%FAT,BAKED,WO/DRIPPINGS, group Finfish and Shellfish Products: vitamin_b12_ug 90% retained, thiamin_mg 90%, vitamin_b6_mg 90%, folate_total_ug 90%; USDA-RETN-R6:2309 FINFISH,<5%FAT,FRIED,WO/COATING: vitamin_b12_ug 90% retained, thiamin_mg 85%, niacin_mg 100%
   USDA Table of Nutrient Retention Factors, Release 6, 2007, Retn_Codes 2301 and 2309 · checked 2026-10-02
5. stro-r4-05 · meta-analysis of RCTs
   Meta-analysis of data from 18 to 21 eligible crossover and parallel-design RCTs with a total of 1392 to 1456 participants found triacylglycerol-lowering effects for lean fish compared with no fish consumption. Lean fish intake showed no significant differences related to total cholesterol or lipoprotein levels.
   Nutr Rev, 2021 · checked 2026-10-02
6. stro-r4-06 · RCT
   LDL level was increased in the supplementation group, while it was significantly reduced in the dietary-fish group (+18.7 ± 24.97 vs. -22.75 ± 27.28, P < 0.001).
   Nutr Diabetes, 2017 · checked 2026-10-02
7. stro-r4-09 · umbrella review
   Moderate-quality evidence suggested that each 100-g/d increment in fish consumption was associated with a lower risk of all-cause mortality (SRR: 0.92; 95% CI: 0.87, 0.97), cardiovascular mortality (SRR: 0.75; 95% CI: 0.65, 0.87)
   Adv Nutr, 2020 · checked 2026-10-02
8. stro-r4-03 · FDA monitoring data
   WEAKFISH (SEA TROUT) | 0.235 | 0.157 | 0.216 | ND | 0.744 | 46 | FDA 1991-2005
   FDA, Mercury Levels in Commercial Fish and Shellfish (1990-2012) · checked 2026-10-02
9. stro-r4-12 · claims register search
   claims_search.py and euclaims_search.py for seatrout, Cynoscion, weakfish, sea trout, fish consumption: 0 results in 21 CFR 101 and 0 of 2330 EU register entries
   EU Register on nutrition and health claims, snapshot 2026-09-21; 21 CFR 101 · checked 2026-10-02
10. stro-r4-07 · meta-analysis of RCTs
    Meta-analysis was possible only for vitamin D (25(OH)D, 1,074 participants), showing a pooled mean difference of 4.08 nmol/L (95% CI: 1.73-6.43) favoring fish consumption
    Front Nutr, 2026 · checked 2026-10-02
11. stro-r4-10 · risk modeling
    Using the EPA Reference Dose of 0.1 ug/kg day as a methylmercury threshold, The fish intake threshold for harm converts to 27 g/day (for a selection of common commercial fish averaging 0.23 ppm MeHg) to 65 g/day for someone choosing fish low in MeHg (0.1 ppm).
    Neurotoxicology, 2005 · checked 2026-10-02
12. stro-r4-11 · meta-analysis
    A significant inverse association was found between fish consumption and depression risk (RR = 0.79, 95% CI: 0.73 to 0.86). A similar association was observed for pregnancy-related depression (RR = 0.78, 95% CI: 0.69-0.89).
    Nutrients, 2025 · checked 2026-10-02
13. stro-r4-13 · evidence gap
    corpus_search.py seatrout: 0 records; Cynoscion OR weakfish OR sea trout only via fish consumption; cofid_search, fndds_search, variability_search seatrout: nothing; retention R6: selenium, protein not in release
    Bioma corpus search, PubMed snapshot 469432, 2026-10-02 · checked 2026-10-02