This article is part of a package on ethical seafood. For mouth-watering recipes, sustainable seafood news, and myriad resources to help readers stay informed and eat sustainably visit www.utne.com/Seafood.

When you are far from the seashore, cheap seafood is suspect seafood. It was probably farmed, and may have gone through several cycles of freezing and re-thawing before getting to your table.

Avoid fish that has traveled too far. The more fuel used to ship it, the less inclined you should be to buy it.

Avoid long-lived predator fish (sharks, swordfish, Chilean sea bass, tuna), which tend to have the highest levels of mercury.

Avoid farmed shrimp, tuna, salmon, and other species that are fattened with other fish; they tend to have higher levels of dioxins and other persistent organic pollutants. Favor tilapia, carp, catfish, and other species that are fed vegetable, rather than animal, protein.

In North America and Europe, opt for domestically farmed seafood. (Standards on additives, water quality, and environmental impact tend to be higher.)

If you have a choice, favor organically farmed salmon, cod, and trout; stocking densities are lower, and they tend to be treated with fewer chemicals.

Finally, opt for seafood at the lower end of the food chain, from mackerel down to oysters. Bottomfeeding is better for your health and for the long- term health of the oceans.

Excerpted from Bottomfeeder: How to Eat Ethically in a World of Vanishing Seafood by Taras Grescoe; www.tarasgrescoe.com. Copyright © 2008 by Taras Grescoe. Reprinted with permission of Bloomsbury USA.