It depends on the fish. Low in saturated fat and swimming with high-quality protein and omega-3 fatty acids, certain species are indeed the perfect health food. But modern aquaculture has bred some nutrients out of many fish. Take salmon. If it’s labeled “wild” or “Alaskan,” eat as much as you can afford. But if it’s farmed (Atlantic) salmon, you’re closer to eating chicken or beef from a feedlot than you might think. Most fish farms—salmon or otherwise—use pellets made of corn and soy as feed, which negatively impacts the nutritional composition of the meat, lowering its omega-3 content. Farmed salmon can also contain up to 10 times more “persistent organic pollutants”—dioxins, PCBs, etc.—than wild salmon, according to research by environmental scientist Ronald Hites, PhD, of Indiana University.