Mercury in fish

Mercury is a metal which occurs naturally in the environment, including within the air, soil and water. Mercury builds up in the aquatic food chain, making fish in particular, a source of mercury.

Why is mercury harmful?

Mercury is toxic to humans and is particularly harmful to babies in utero. During pregnancy, the mercury which a mother consumes naturally from the food supply, can cross the placenta and affect the baby. Too much mercury can affect the development of the baby’s brain and nervous system. These affects may not be diagnosed until developmental delays are noticed in the child, such as delayed walking or talking.

Infants and young children (up to 6 years of age) are also vulnerable to the harmful effects of mercury due to their rapidly growing bodies.

Should I avoid all fish?

No. Fish is a great source of protein, iodine, vitamin B12 and omega 3 fats making it an important part of a healthy diet for pregnant women. However, there are some fish that pregnant women should limit eating.

Bigger, predatory fish (those that eat other fish), contain more mercury than smaller fish. This is because they are taking on the mercury from the fish that they eat in addition to that which they absorb from their environment.

What is a safe amount of fish?

Food Standards Australia New Zealand have provided advice on safe consumption of fish based on the latest scientific information. Their advice for pregnant women, women intending to become pregnant within the next six months and young children (up to 6 years of age) is as follows:

• Limit to one serve (150g) per fortnight – shark (flake) or billfish (swordfish, broadbill and marlin) and no other fish eaten in that fortnight.
• Limit to one serve (150g) per week – orange roughy (deep sea perch) or catfish, and no other fish eaten that week.
• Eat 2–3 serves per week – of any other fish or seafood that is not listed above (for example, salmon or tuna).