These days, more than one third of the fish we eat come from fish farming operations. While farmed fish greatly increase the availability of a number of species, they are exposed to high levels of disease as well as toxins and fungicides in their holding areas.
According to the Center for Food Safety, farmed fish accumulate PCBs (toxic industrial compounds banned in 1970) faster than wild fish. Fish farms are largely unregulated, meaning there’s no telling what kinds of antibiotics and dyes are added to the water. On top of this, mass-produced fish can have a number of negative environmental effects, including water contamination and species endangerment. Plus, the small fish that compose the diets of larger, farmed fish such as salmon are being over-fished in order to supply feed.
Try to buy wild fish whenever possible, and don’t be afraid to ask your fish seller where his fish comes from if it’s not labeled. Not all farmed varieties are necessarily bad for the environment; some, such as catfish, eat only water plants and are less disease-prone than their carnivorous counterparts—stay away from farmed Atlantic Salmon and ranched tuna. All fish, however, are susceptible to contamination by mercury and other toxins, and fish, especially the large ones higher on the food chain, should always be eaten in moderation.