For most people, the level of mercury absorbed by eating fish and shellfish is not a health concern. Overall, fish and shellfish are healthy foods. They contain high-quality protein and other essential nutrients and contain omega-3 fatty acids, a type of essential fatty acid. A balanced diet that includes fish and shellfish can contribute to heart health and children's growth and development.
All fish and shellfish contain traces of mercury. But some contain high levels. Eating large amounts of these fish and shellfish can result in high levels of mercury in the human body. This is especially harmful to young children and pregnant women.
Since wild caught fish eat varied diets some fish may be much higher in mercury than others. For this reason we test the fish on our grocery for mercury levels. Scroll to the bottom of this page for the results.
Mercury accumulates in the tissue over time. For this reason bigger predatory have more mercury than smaller fish that are lower on the food chain. Fish with longer life spans are also higher in mercury. Here's a value chart with fish that tend to be high in mercury versus the amount of omega 3's they contain:
Orange roughy is a fish that has a lifespan of 100 years and is thus high in mercury. Tuna, Marlin, Shark, Swordfish are all predatory fish and high up the food chain and so too they accumulate a lot of mercury. Small fish such as anchovy, sardines are high in omega 3 and very low in mercury making it the best choice to eat. While cod/haddock/perch are all low in mercury too, they contain less omega 3's like EPA/DHA, but they are of course still a healthy choice.
I want my two year old son to eat enough fish as omega3, DHA and EPA are essential to a proper brain development. Nearly 60% of the human brain consists of fat. During his first year his brain grew 3 times its size. So it seems like a good idea to eat plenty of fish, since fish is by far the most abundant source of EPA/DHA omega 3 fatty acids. You can find omega 3 in plant foods like flax seeds, but they are mostly ALA, which is very poorly converted to DHA by the human body.
So fish it is, but I don't want him to consume large amounts of mercury, therefore I am very particular about which fish to serve. For my son I stick mostly to wild Alaskan Sockeye Salmon, tinned Norwegian Sardines and occasionally hake or perch. For myself I also get the majority of my fish intake from sockeye salmon, coho salmon and sardines, but I every now and then I eat some tuna or orange roughy as they are absolutely delicious. I just don't eat it more than once a week and in moderate quantities.
From our test we saw that wild Alaskan sockeye salmon has roughly 0.041μg/g and sardines has 0.047μg/g. These numbers place it in the best choices and you can eat your heart out on these. Our blue hake(hoki) and smooth dory from New Zealand range between 0.118μg/kg and 0.195μg/kg. This is 3 to 4.5 times higher, but still places it in the best and good choices category. We also tested our Orange Roughy and it came back at 0.753μg/kg. So we recommend to eat this fish only once a month and not weekly and to avoid entirely for small children or if you're pregnant.