Mercury in fish
Health benefits of fish
Fish is a nutritious food. It is low in saturated fat, and is an excellent source of:
- essential omega-3 fatty acids
- some vitamins.
However, some fish can also contain mercury, which occurs naturally in sea water.
When to be aware of mercury in fish
Different fish species contain different levels of mercury.
Most people do not need to be concerned about mercury in fish as they are not exposed to high enough levels to cause harm. Our bodies eventually excrete any mercury build up over time.
However, some types of fish contain high levels of mercury. If you're pregnant or eat a lot of fish, you need to be more careful.
Eating fish when pregnant
Eating fish during pregnancy is recommended as part of a well-balanced diet, because it is a nutritious food for you and your growing baby.
However, MPI advises that women who are pregnant or are considering pregnancy, limit their consumption of types of fish that contain higher levels of mercury.
These types of fish include:
- dogfish (excluding rig)
- Lake Rotomahana trout
- lake trout from geothermal regions
- school shark (greyboy, tope)
- marlin (striped)
- southern bluefin tuna
Breastfeeding and eating fish
Breast milk is not a significant source of mercury.
Amount of fish that pregnant women can eat safely
Some fish species can be eaten without restriction but others should be eaten less often. MPI has prepared a list for reference.
How mercury builds up in fish
Mercury occurs naturally in the environment and builds up in fish over time.
Mercury levels in fish vary between species depending on habits and feeding patterns. Most species build up only low levels of mercury over their lives.
Predatory fish at the top of the food chain, such as shark and swordfish, tend to accumulate higher levels of mercury. In fish species that live for a long time, high mercury levels are often found in older fish.
Freshwater fish, such as trout, which live in lakes and rivers supplied by geothermal water may also accumulate higher levels of mercury because mercury is commonly found in volcanic emissions.
Fish caught in some lakes are also high in mercury and consumption should be limited to no more than one serving a week or fortnight. However, trout caught in Lake Taupō are not high in mercury.
More information is available in the list of safe food for pregnant women.
Mercury not high in canned products
Canned fish are not a higher risk for mercury than fresh fish. The mercury content of fish is not affected by processing techniques such as cooking, canning or freezing.
The tuna and small fish species (such as sardines, pilchards and herring) sold in cans are short-lived species which accumulate only low amounts of mercury. Larger tuna are sold fresh.
Fish oil products and supplements are not a major source of mercury in our diet, and MPI does not recommend you restrict your intake based on concerns about mercury.
Recommendations are for New Zealand only
Australia has its own species-specific recommendations for which fish types are safe to eat during pregnancy. Many of the fish species sold in Australia are different to those available in New Zealand (such as barramundi and catfish).
Most come from different fishing grounds to those sold here and have different exposure levels. In addition, some fish with the same common name are different species. For example 'orange roughy' in Australia is also known there as 'sea perch' – but sea perch sold in New Zealand is an unrelated species.
Who to contact
If you have questions about mercury in fish, email firstname.lastname@example.org.