There is no doubt that seafood and fish contribute many excellent health benefits and is considered one of the healthiest food groups.

In addition to a wide range of health benefits, their flesh also concentrated methylmercury.

The concentration levels of mercury in fish depend on various factors such as the species, size and age of the specific fish or seafood. It also varies depending on the pollution levels of the waters from which the fish is extracted.

The health benefits of fish and seafood outweigh the risk of mercury exposure if: (1)

• The fish and seafood consumed has low levels of mercury
• It is consumed within the weekly recommended limits

Statistics

In the U.S. population, the total fish and seafood consumption is (2):

• 39% – 43% of mercury comes from tuna
• Swordfish (8%)
• Pollock (8%)
• Shrimp (5%)
• Cod (4.5%)

Mercury recommended daily limit

The current safe daily limit for mercury intake has been established to be 0.1 micrograms per kg of body weight. The following table shows some examples of safe weekly limit of mercury per body weight:

Body Weight (kg)	Limit of mercury (mcg/week)
50	35
60	42
70	49
80	56
90	63
100	70

The general recommendations for the maximum safe limit intake of mercury vary slightly from country to country since fish may be caught in different waters with different pollution levels.

How much fish should you eat per week?

In summary, the recommendations for an adult are 2-3 serves (1 serve = 150g) of fish per week. If you wish to eat more than that, you should make sure that you include low mercury level species. (3)

For a special group: pregnant, planning to be pregnant or breastfeeding women (1 serve = 150g) and small children (1 serve = 85g) the recommendations are:

• 2-3 serves per week of low mercury small fish or
• 1 serve per week of catfish, orange roughy (deep sea perch).
• Avoid fish high in mercury such as tilefish, shark, swordfish, marlin, and king mackerel. (1, 4)
  Australian authorities allow some intake of these fish (1 serve per fortnight). However, considering the potential dangers, many health professionals advise to avoid them altogether. (5)

NOTE: Due to varied levels of mercury in fish and seafood and recent evidence of the health risks associated with low levels of mercury intake the current official recommendations may be undervalued. In addition to following these recommendations, it is important to keep track of the fish consumption using the more detailed list of mercury contents. (6)

Mercury levels in fish

The following table shows the concentration of mercury in different species of fish and seafood in studies conducted between 1990 and 2010: (7)

Species	MEAN (PPM)	MAX (PPM)	mcg in 3 oz serving
TILEFISH  (Gulf of Mexico)	1.45	3.73	123.25
SWORDFISH	0.995	3.22	84.575
SHARK	0.979	4.54	83.215
MACKEREL KING	0.73	1.67	62.05
TUNA (FRESH/FROZEN, BIGEYE)	0.689	1.816	58.565
ORANGE ROUGHY	0.571	1.12	48.535
MARLIN *	0.485	0.92	41.225
MACKEREL SPANISH (Gulf of Mexico)	0.454	1.56	38.59
GROUPER (ALL SPECIES)	0.448	1.205	38.08
TUNA (FRESH/FROZEN, Species Unknown)	0.415	1.3	35.275
TUNA (FRESH/FROZEN, ALL)	0.391	1.816	33.235
BLUEFISH	0.368	1.452	31.28
SABLEFISH	0.361	1.052	30.685
TUNA (FRESH/FROZEN, ALBACORE)	0.358	0.82	30.43
TUNA (FRESH/FROZEN, YELLOWFIN)	0.354	1.478	30.09
BASS CHILEAN	0.354	2.18	30.09
TUNA (CANNED, ALBACORE)	0.35	0.853	29.75
CROAKER WHITE (Pacific)	0.287	0.41	24.395
HALIBUT	0.241	1.52	20.485
WEAKFISH (SEA TROUT)	0.235	0.744	19.975
SCORPIONFISH	0.233	0.456	19.805
MACKEREL SPANISH (S. Atlantic)	0.182	0.73	15.47
MONKFISH	0.181	0.289	15.385
LOBSTER (Species Unknown)	0.166	0.451	14.11
SNAPPER	0.166	1.366	14.11
BASS (SALTWATER, BLACK, STRIPED) [3]	0.152	0.96	12.92
PERCH (Freshwater)	0.15	0.325	12.75
TUNA (FRESH/FROZEN, SKIPJACK)	0.144	0.26	12.24
TILEFISH (Atlantic)	0.144	0.533	12.24
SKATE	0.137	0.36	11.645
BUFFALOFISH	0.137	0.43	11.645
TUNA (CANNED, LIGHT)	0.128	0.889	10.88
PERCH OCEAN *	0.121	0.578	10.285
COD	0.111	0.989	9.435
CARP	0.11	0.271	9.35
LOBSTER (NORTHERN / AMERICAN)	0.107	0.23	9.095
SHEEPSHEAD	0.093	0.17	7.905
LOBSTER (Spiny)	0.093	0.27	7.905
WHITEFISH	0.089	0.317	7.565
MACKEREL CHUB (Pacific)	0.088	0.19	7.48
HERRING	0.084	0.56	7.14
JACKSMELT	0.081	0.5	6.885
HAKE	0.079	0.378	6.715
TROUT (FRESHWATER)	0.071	0.678	6.035
CROAKER ATLANTIC (Atlantic)	0.065	0.193	5.525
CRAB [1]	0.065	0.61	5.525
BUTTERFISH	0.058	0.36	4.93
FLATFISH [2*]	0.056	0.218	4.76
HADDOCK (Atlantic)	0.055	0.197	4.675
WHITING	0.051	0.096	4.335
MACKEREL ATLANTIC (N.Atlantic)	0.05	0.16	4.25
MULLET	0.05	0.27	4.25
SHAD AMERICAN	0.045	0.186	3.825
CRAWFISH	0.033	0.051	2.805
POLLOCK	0.031	0.78	2.635
CATFISH	0.025	0.314	2.125
SQUID	0.023	0.07	1.955
SALMON (FRESH/FROZEN) *	0.022	0.19	1.87
ANCHOVIES	0.017	0.049	1.445
SARDINE	0.013	0.083	1.105
TILAPIA *	0.013	0.084	1.105
OYSTER	0.012	0.25	1.02
CLAM *	0.009	0.028	0.765
SHRIMP *	0.009	0.05	0.765
SALMON (CANNED) *	0.008	0.086	0.68
SCALLOP	0.003	0.033	0.255

Tips on limiting mercury intake

• Eat fish and seafood with a low level of mercury and high level of omega-3 fatty acids such as sardines, mackerel, herrings, Atlantic salmon, canned salmon and “light tuna”.
• Avoid fish with a very high mercury concentration such as shark (flake), marlin, swordfish, king mackerel and tile-fish. Although it is most likely that the fish you eat contains mercury levels as shown in the “average amount” column, you can never be sure. Some fish have shown to have much higher levels of mercury shown in the “maximum amount” column. (8)
• Use the above table of mercury levels in various fish and seafood to make your choices and to keep track of what you eat.

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You will find a summary of the most common nutrition myths and evidence-based nutrition facts here.