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Fish Farms

Not all fish are created equal


If I found myself stranded on a desert island, I'd have the assurance of an unlimited source of the healthiest food I could imagine: omega-3 fatty acids and high quality protein from wild fish. Fish may just be the stuff of life. Its healthy fats are essential to optimal cardiovascular function, joint health, brain function, and blood sugar metabolism.

If I found myself stranded on a desert island, I’d have the assurance of an unlimited source of the healthiest food I could imagine: omega-3 fatty acids and high quality protein from wild fish.

Fish may just be the stuff of life. Its healthy fats are essential to optimal cardiovascular function, joint health, brain function, and blood sugar metabolism. By adding a few tropical fruits I could probably live a long and healthy life on my desert island. Of course, if I were lucky enough to find myself far away from the “civilized world,” I could also improve my chances of finding fish free of toxins.

Toxic Mash

Sadly most of the fish available in North American markets come from fish farms, which are little more than cesspools of toxic sludge that pollute our water and, consequently, our bodies when we consume these fish. About one third of the world’s seafood is produced by fish farms, most notably, nearly all the catfish and trout and half of the shrimp and salmon so important to human nutrition. It’s cheap: farmed salmon can be $4 to $5 a pound cheaper than wild-caught salmon, but the price may be too high in terms of our health and to the health of our environment and wild fish populations.

While farmed fish is still a rich source of omega-3 fatty acids, it’s strangely paradoxical to think that the food most often recommended for its multitude of health benefits can be so insulting to our body chemistry. In a landmark 2002 study, Canadian researchers found that a single serving of farmed salmon contains three to six times the World Health Organization’s daily intake limit for dioxin and polychlorinated biphenyls (PCBs).

These chemicals, once used in the manufacture of electrical and heating equipment, paints, plastics, rubbers, dyes, and many other substances, were banned in 1977 after the US Environmental Protection Agency (EPA) called them “probable human carcinogens.”

However, PCBs are still present in water and soil. In its December 26, 2005 issue, U.S. News and World Report reported that farmed salmon are often raised on fish pellets derived from fish contaminated with PCBs.

A study in the November 2005 issue of the Journal of Nutrition reported that contaminant levels in farmed salmon from certain regions increase the risk of cancer enough to outweigh the health benefits. The study showed that farmed salmon from South America, specifically Chile, had the lowest level of pollutants, followed by those from North America. Europe had the highest level, according to David Carpenter, MD, coauthor of the study and director of the Institute for Health and the Environment at the University at Albany’s School of Public Health. Pacific wild salmon also has some contaminants from the environment, specifically mercury, but at a low enough level that the health benefits outweigh the risks.

Mercury can be a big problem with farmed fish. Purdue University nutritionists found that eating as little as one fish sandwich from farmed fish weekly could give a 130-lb (60-kg) adult 40 percent of the safe maximum weekly mercury exposure.

Fish farms are most often composed of huge net enclosures in the open sea. Disease is rampant in these crowded pens. Large quantities of chemicals are used in the pens, including antibiotics, pesticides, hormones, anaesthetics, vitamins, minerals, and antiparasitical substances. The use of antibiotics is particularly hazardous to the health of humans and fish since it promotes the spread of antibiotic resistance. The potent antiparasitic drug called ivermectin (used to kill sea lice) is also known to kill some species of shrimp. Not only are these potentially toxic substances incorporated into the tissues of the farmed fish, but tides and simple wave action sweep these chemicals out of the nets and into the open seas.

Damage to the Environment

Within a few years after large-scale fish-farming operations began in Canada, shrimp fishermen began pulling up traps full of a deadly mixture of fish feces, excess antibiotic-laden fish feed, and decayed salmon carcasses that had drifted out of the pens. It’s estimated that one pen of 200,000 fish produces as much fecal waste as a city of 25,000 people.

In British Columbia, many inlets are caged off for huge Atlantic-salmon farms. These fish have been genetically modified with voracious appetites to encourage fast growth. Although fish farmers assure consumers they have contained the fish, an estimated 40,000 to one million have already escaped. Biologists have found Atlantic salmon from the farms in 77 British Columbia streams. When these super-fish get into the wild, they compete unfairly for food resources, causing an increased rate of starvation among wild fish.

Yet business is booming for Canadian fish farmers. In early 2002 the Canadian government lifted its seven-year moratorium on expanding fish farms in British Columbia. By 2003 there were 85 fish farms in operation in British Columbia and 90 applications pending. The government has stated its intention to quadruple the province’s salmon production by 2013.

Part of the allure of fish farming is to reduce the pressure on the world’s oceans, but that may be wishful thinking. Fish farming is an inefficient means of producing protein. A February 6, 2003 article in The Christian Science Monitor notes that raising carnivorous fish like salmon and shrimp may actually reduce the numbers of wild fish, since it takes 2 1/2 pounds (about 1 kg) of ground-up fish to make one pound of farmed salmon.

Monitor Your Mercury

There seems to be a Gordian knot around fish consumption–and the very experts on whom we rely for the best possible information are sending us mixed messages about the best way to get the healthy fats that fish provide.

Most health experts recommend being conservative about toxin exposure, and some advise avoiding fish altogether. Despite many nutritionists extolling the virtues of high fish consumption, the FDA strongly recommends limiting the amount of fish we eat, although an FDA health advisory issued in March 2004 does not distinguish between farm-raised and wild-caught fish.

The FDA recommends that all women who are pregnant, may become pregnant, nursing mothers, and young children abstain completely from fish with high levels of mercury contamination, which may be particularly harmful to unborn babies and the developing nervous system of young children. The FDA advisory recommends eating no more than 12 ounces (341 g) of fish and shellfish lower in mercury (see sidebar). It also advises keeping up to date on local fish safety warnings, and, if there is no advisory available, not to eat more than six ounces (170 g) of local-caught fish weekly.

Yet many of us are still getting too much mercury–some of it due to the 40 tons of mercury released into the atmosphere annually by coal-fired power plants. The US Centers for Disease Control and Prevention released a study in November 2005 that showed fully six percent of US women of childbearing age had mercury levels above the levels that could put them at risk for nervous system defects.

Some natural health advocates say several more fish should be added to the list of fish to avoid, including tuna steaks, sea bass, oysters form the Gulf of Mexico, marlin, halibut, pike, walleye, white croaker, and largemouth bass. They urge the FDA to expand the list of fish to be avoided and those acceptable for limited consumption.

You can safely eat one or two servings of wild-caught fish weekly if you aren’t in one of the risk groups. With this moderate amount, you can also consider increasing your omega-3 fatty acid intake by taking supplements, which don’t pose the same risk since they are purified of mercury and other contaminants often found in fish.

Get Your Healthy Fats a Safer Way

  • Look for a good brand of fish oil, and throw it away if you get a fishy belch-back.
  • Krill oil, made from tiny fish that live in the cold, pure Antarctic waters, is a safe option.
  • Cod liver oil has the added benefit of being one of the few food sources of vitamin D.
  • If you’re thinking “yuck” when you think of cod liver oil, think again. New technology has eliminated the “yuck” factor and given it a rather pleasant lemony taste.
  • If you’re still squeamish, cod liver oil is even available in capsules that leave no after taste.

Mercury Levels in Fish

  • High (shark, shrimp, swordfish, king mackerel, tilefish)
  • Low (canned light tuna, wild salmon, pollock, wild catfish)


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