Author: Ms. Agnes Lam, Nutritionist at HK BioTek
We talked about the pros of eating deep sea fish in the last issue, but we often avoid eating deep sea fish due to its mercury level. So how should we choose which deep sea fish, and how much should we eat, as to benefit from its advantages without intaking excess intake of mercury? The table above can serve as a reference for every smart consumer when choosing deep sea fish.
The mercury level in fish depends on its species, age, foraging mode and habitat. Those which are older or in higher position of the food chain (fish larger in size) usually contains more mercury in their body.
Table 1: Fish traffic light
|Red light||Green light|
|Bluefin Tuna||Rainbow Trout|
|Source: Hong Kong Centre for Food Safety, US FDA, British Columbia Ministry of Health|
Those listed in the ‘red light’ column are fish that contains higher average mercury level (Table 2), and should not be frequently consumed. The maximum safe intake level of mercury, set by the Food and Agriculture Organization of the United Nations and the WHO Joint FAO/WHO Expert Committee on Food Additives (JECFA) in 2003, was set at 1.6 microgram per kg weight per week. For example, if an adult of 60kg body weight intake 3 ounces (85g, around size of a palm) tilefish, the mercury level already exceeds the maximum safe level by 30%. As the impact of mercury is particularly susceptible to pregnant women, women preparing for pregnancy and infants, people falling in these groups should avoid eating fish that might contain high level of mercury.
Fish listed in the ‘green light’ column are those with lower average mercury level (Table 2), and can be consumed regularly and in varieties. The American Heart Association recommends weekly intake of deep sea fish for 2-3 times, 3 ounces each to meet the requirement of recommended intake of omega-3.
Table 2: Average mercury level and omega-3 content of different kinds of fish
|Species||Average mercury level
|Fish with higher mercury level|
|Swordfish||970 – 1820||0.97|
|Shark||540 – 1500||0.83|
|Marlin||1100 – 1430||–|
|Big-eye Tuna||639 – 740||1.36|
|Bluefin Tuna||730||1.17 – 1.50|
|Fish with lower mercury level|
|Salmon||10||1.10 – 1.90|
|Sardine||13||1.30 – 2.00|
|Atlantic Mackerel||50||1.10 – 1.70|
|Rainbow Trout||70||0.84 – 0.98|
|Source: Hong Kong Centre for Food Safety, US FDA, American Heart Association|