Avoid big fish at the top of the marine food chain—tuna, swordfish, shark—because they’re endangered, and because they often contain high levels of mercury. Fortunately, a few of the most nutritious wild fish species, including mackerel, sardines, and anchovies, are well managed, and in some cases are even abundant. Those oily little fish are particularly good choices. According to a Dutch proverb, “A land with lots of herring can get along with few doctors.”
