Fish and shellfish are highly nutritious foods that can contribute much to a healthy diet.
Rich in protein, iodine and some B group vitamins plus vitamins D and E. Fish is low in saturated fat but contains essential Omega 3 fatty acids (EPA and DHA) that are believed to be important for cognitive development and function.
While fish can also contain some mercury it is still possible to enjoy the health benefits of eating fish and keep the exposure to mercury within safe limits.
Women who are pregnant or considering pregnancy should take particular care to keep within the safe limits as described below.
Concerns regarding Mercury
Mercury occurs naturally in the environment and is found in soil, rocks and water. It is also an environmental contaminant from industry and mining activities.
Mercury is found in three main forms: elemental, inorganic and organic. Methyl mercury is the organic form and the one that is most toxic. This is also the type of mercury that accumulates in fish.
Normally people are not exposed to high enough levels to cause neurological damage because our bodies excrete mercury over time and so accumulation is seldom a problem.
However when fish that have a high level of methyl mercury are eaten, the mercury is absorbed easily into the blood stream and is distributed around the body. Unborn babies and infants are more sensitive to mercury’s harmful effects and so it is important to limit their exposure, particularly to those fish with the highest mercury levels.
Mercury levels in fish
Mercury levels differ regionally and so recommendations vary around the world.
The fish habitat
Mercury levels in fish also depend on the type of fish and their feeding habits. Most fish accumulate only small amounts of mercury throughout their life by eating plants and other organisms in the water that contain mercury. However predatory fish at the top of the food chain, such as shark and swordfish, live longer and so have the time to eat more fish and therefore accumulate higher mercury levels.
Regional variation
Mercury is also found to be higher in volcanic areas. So freshwater fish such as trout, that live in lakes supplied by geothermal water, should be limited to no more than one serving per week or fortnight.
MPI Recommendations in New Zealand
The MPI have identified the many commonly eaten fish in NZ where there is little concern regarding mercury and they can be eaten freely.(1)
- Mixed fish (e.g. battered fish or fish fingers) are also low in mercury and can be eaten without restriction (1)
- The Australian New Zealand Food Standards Code has safe upper and lower mercury limits for fish. For low mercury fish the limit is 0.5mg/kg and the higher levels the limit is 1.0mg/kg.(2)
- A limit for crustacean and mollusks has also been established at 0.5mg/kg (2)
Table 1
| No Restriction Necessary | Low Mercury Fish | High Mercury Fish |
| Anchovy | Albacore tuna | Cardinal fish |
| Arrow squid | Alfonsino | Dogfish (excluding rig) |
| Barracouta | Bass | Lake Rotomahana trout |
| Blue cod | Bluenose | Lake trout from geothermal regions |
| Brill/Turbot | Gemfish | School shark (Greyboy, Tope) |
| Brown trout from Lake Ellesmere | Ghost sharks | Marlin (striped) |
| Cockles | Hake | Southern bluefin tuna |
| Eel, long or short finned | Hapuka (Groper) | Swordfish |
| Elephant fish | Javelin Fish | |
| Flounders | Kahawai | |
| Gurnard | Kingfish | |
| Hoki | Lake Taupo trout | |
| John Dory | Leatherjacket | |
| Monkfish or stargazer | Lemon sole | |
| Mussels (green and blue) | Ling | |
| Orange perch | Mackerel (blue and jack) | |
| Oysters (Bluff* and Pacific) | Orange roughy | |
| Parore | Oreo dories | |
| Rainbow trout from non-geothermal regions | Red cod | |
| Salmon (farmed) | Ribaldo | |
| Scallops* | Rig (Lemonfish, Spotted dogfish) | |
| Skipjack tuna* | Rock lobster | |
| Sole (except Lemon sole) | Sea perch | |
| Southern blue whiting | Silverside | |
| Surf clams (eg, tuatua) | Skate | |
| Tarakihi | Smooth oreo | |
| Toothfish (Antarctic) | Snapper | |
| Warehou (common, silver and white) | Sprats | |
| Whitebait (Inanga | Trevally |
*Note Pregnant women should limit their intake of Bluff oysters and Queen Scallops due to higher levels of cadmium. (1)
* No data is available for Yellow-fin tuna (1)
Recommendations intakes in Australia and New Zealand
Adults and older children
- Can consume 150g servings of a variety of fish 2-3 times a week.
- If fish containing higher levels of mercury (e.g. shark, swordfish or marlin) are eaten then this should be limited to one serving per week but no other fish should be eaten during that week. (2)
Pregnant and breast feeding women
- Can consume 150g servings of a variety of fish 2-3 times a week.
- Consumption of low mercury fish ( e.g. Orange Roughy/ Sea Perch) should be limited to 150g/week and to have no other fish that week.
- If consuming high mercury fish (e.g Shark/Flake or Billfish/Swordfish/ Broadbill or Marlin) limit consumption to 150g/fortnight but have no other fish for that fortnight. (2)
- Pregnant women should limit their intake of Bluff oysters and Queen Scallops due to higher levels of cadmium. The MPI also remind women that shellfish should never be eaten raw in pregnancy. (1)
- Breast Feeding women can resume their normal diet once their baby is born as breast milk is not considered a significant source of mercury. (1)
- Note this information has been updated -please check MPI recommendations below
Children up to the age of six years
- They are encouraged to consume 75g servings of a variety of fish 2-3 times a week.
- Consumption of low mercury fish (e.g. Orange Roughy / Sea Perch) should be limited to 150g/week and to have no other fish that week.
- If consuming high mercury fish (e.g Shark/Flake or Billfish/Swordfish/ Broadbill or Marlin) limit consumption to 150g/fortnight but have no other fish for that fortnight. (2)
Food processing and mercury
As the mercury is bound to the protein in the muscles of fish it is not affected by food processing methods such as cooking, canning or freezing.
Canned or cooked fish
- These are not a higher risk than raw fish.
- Tuna used in canning and small fish such as sardines, herrings and pilchards are short-lived species which accumulate low levels of mercury.
Fish oils and supplements
- These are not a major source of mercury in the diet.
Dried fish
- Certain ethnic populations may be at higher risk for mercury poisoning if they are consuming imported fish from Asia, especially dried fish.(2)
Overseas travellers
As mercury levels vary regionally it is important that, if consuming fish in countries outside NZ and Australia, you consult the local health authorities if you have concerns regarding specific mercury levels in fish. Particularly if you are pregnant or caring for young children.
If you would like to discuss your family’s diet then contact us today
Note Updated information for pregnant women
2018 List of safe food in pregnancy
For more information on fish and food safety read Lea’s article on:
Fish for good health http://www.leastening.com/articles/food-fluids/fish-for-good-health.html
Fish for good child nutrition http://www.leastening.com/articles/children/fish-for-good-child-nutrition.html
Listeria http://www.leastening.com/articles/children/listeria.html
References
- Mercury in fish report. Ministry of Primary Industries (MPI) http://www.foodsmart.govt.nz/whats-in-our-food/chemicals-nutrients-additives-toxins/specific-foods/mercury-in-fish/
- Mercury in fish Food Standards Code 2011 http://www.foodstandards.govt.nz/consumer/chemicals/mercury/pages/default.aspx
- Food safety. Agriculture and Fisheries http://www.pennutrition.com/KnowledgePathway.aspx?kpid=2536&trid=16798&trcatid=42
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