Is There Any Fish That's Okay to Eat?

Writer Mark Kurlansky did a Q&A on sustainable seafood and ocean contamination over at the New York Times, and someone asked him if there's any fish that is "totally o.k. to eat." Kurlansky doubts it, but thinks herring's a good bet: "Many contaminants such as heavy metals intensify up the food chain — i.e. a tuna that eats cod that have eaten herring that have mercury will have a lot more mercury than the herring — it is a healthy idea to eat the herring." [NYT]