As a general rule, small, short-lived, non-predatory fish low on the underwater food chain have the lowest amounts of mercury. Smaller fish like sardines aren’t big enough to eat more than plankton, and fish like the famous tilapia eat a lot of algae, for example. Longer-lived predatory fish, such as tuna, have higher mercury levels because they eat many small fish with small amounts of mercury, which then accumulate in larger, longer-lived fish. live fish In other words, the higher up the food chain you go, the more mercury you consume. Tuna live for about 15 years, so mercury builds up over time in their tissues; sardines only live around five years.
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But what explains the difference between canned and fresh fish? Usually, smaller types of fish are used in canned food. Fish like salmon have several subspecies: pink salmon is a common choice for canned salmon, and they are small fish weighing only about 4 pounds on average. Not surprisingly, pink salmon eat a lot of zooplankton. Meanwhile, larger Atlantic salmon are usually sold fresh and are around 10 pounds, and their larger size means they can eat other fish and crustaceans, which are more mercury-heavy meals.
