Good news for consumers: Pink salmon -- yes, the cheap, trash salmon you buy in cans -- is tops when it comes to cleanliness, according to research by Dr. Michael Ikonomou of Canada's Department of Fisheries and Oceans. And if you don't like pink, sockeye -- yes, even in cans -- is also a healthy choice, assuming you select the right containers.

The catch with salmon and all oily fish is that the healthy omega-3s you're after and the pollutants from industry you're trying to avoid BOTH live in fat. That means you need to eat enough fish to get your omega-3 ration, but limit your intake to avoid too many toxins.

Because all the species of salmon differ in the quantity and quality of their fat, your weekly ration will depend on the type you're eyeing. With sockeye, you'd need around a small can a week. With pink, you could almost double that amount. Why the difference? Sockeye is fattier and lives longer, hence it accumulates more pollutants.

1/ And what about fresh salmon? The wild Pacific? It's almost salmon season in the Pacific Northwest -- those few months of the year when the fish are running and consumers can finally find fresh wild Pacific salmon in stores everywhere. Sockeye and pink are just two of the many species of wild Pacific salmon that live in the cold waters of the north Pacific -- from northern California up to Alaska -- and beyond. Chum, another Pacific species, is as clean as pink but so lean that it lacks omega-3s. And steelhead swims so close to the surface that it rarely gets caught.Then there's coho and Chinook, the king of salmon. Coho and sockeye are similar in fat content; with both, you need about 400 grams of fresh salmon a week for your omega-3 intake. Chinook is the highest in fat of all the wild Pacific species, hence tasty but greatest in pollutants. Cap consumption at 300 grams weekly.

(These recommendations are general: Every single piece of fish you buy will differ in its omega-3 content, and the amounts suggested assume that salmon is your only source of those healthy fats. If you're eating other "3s from the sea," then decrease your salmon.)

Does it really matter where your wild Pacific salmon comes from? Is Alaskan salmon really the best? The Bering Sea in northern Alaska is as pristine as it gets, says Ikonomou. But below that, the waters off southern Alaska and northern British Columbia are similar -- a few small plumes of pollution and population centres dotting an otherwise clean coast. In fact, some of the very best sockeye, according to an Alaskan fish distributor, are from rivers in northern B.C. Offshore pollution, however, is a problem when people and industry abound onshore; and from southern B.C. down to northern California, the waters are hurting. What does that mean for the consumer? Check the source.

2/ And what about Atlantic salmon? It's a species in itself and unlike wild salmon, usually farmed, produced in countries that don't necessarily abut the Atlantic Ocean: Norway (the world's biggest producer), Chile (in second place), other European countries, Canada and to a small extent, the U.S. Because of the concern with pollutants in farmed salmon, experts recommend no more than two portions a week -- 200 to 250 grams maximum.

But unlike wild salmon, the industrial pollutants in farmed salmon have little to do with the waters they're raised in. Their feed consists to a large degree of fish and fish parts, all sources of omega-3s, and what's crucial are the waters surrounding the fish used for feed. Back in the mid 2000s, farmed Atlantic salmon got a bad rap when a study came out showing it was loaded with industrial pollutants. The source of the problem: the feed was manufactured from fish in the filthy Baltic and North Seas.

Over the years, the Europeans have adopted stricter limits on pollutants, and fish feed manufacturers have cleaned up their act, sourcing cleaner species, sometimes decontaminating feeds and substituting plants and, in North and South America, animal parts, including those of chickens and pigs. The result? Today's farmed salmon is cleaner than it was a decade ago. But because the plants and animal parts are full of omega-6 fatty acids, already overabundant in our diets, some experts are concerned that farmed salmon, especially if from the Americas, suffers from omega-6 overload.

And then there's the problem with chemicals. Aquaculture uses a load of them. A large study sponsored in part by the World Wildlife Federation found that pesticides to control parasites, including sea lice, and disinfectants, which have been linked to cancer, are particularly troubling.

One salmon-phile who commented on my blog witnessed fish with "double-sized heads, huge stomachs, no tails and major deformations...being sold at reduced prices" in a local market in Chile. One potential result of chemicals?

Is organic salmon any better? Over the past two decades, several organizations in Europe have adopted standards for organic fish farming. But contrary to what you might think, the movement did not evolve to protect you, the consumer. Its main concern: the environmental effects of fish farming, especially the wholesale vacuuming up of large supplies of fish used for feed. For that reason, organic standards require the feed be made from the trimmings of fish destined for human consumption -- including bones, organs, heads and eyes. (They're full of omega-3s.)

Organic farmers do use fewer chemicals than conventional farmers, but they still use chemicals, to varying degrees. All the organic standards coming out of Europe differ; and while the U.S. and Canada have not yet adopted organic standards, their Whole Foods retail outlets sell salmon under a premium label that has stricter rules on chemical use than many organics.

The main factor contributing to your human health, however, is likely not chemical use but the quality of the feed. And it's impossible to know whether organic feed is cleaner than conventional feed without knowing exactly what fish are used in each feed, in what proportions and where they come from. No manufacturer in its right mind would tell me that. What they did tell me is that organic feed has a higher fish component than regular feed, with its animal and plant substitutes. And that brings us to the bottom line: The high proportion of fish used in organic feed increases the possibility of more omega-3s but also of more pollutants; hence, it's wise to follow the same limits as conventional -- 200 to 250 grams max a week. You might even want to err on the low side.

To get your omega-3 ration, however, you have to eat the fat in salmon. And where is that? It's not in the little white zigzagging lines you see in the fresh salmon. Those are cartilage, which act as borders between the muscles. In fact, you can't see most of the fat in salmon -- it's distributed throughout the pinky flesh. But if you buy a salmon steak that's cut from the tail end of the salmon, you'll see dark red triangles on either side of the steak. That's an area of fat called the lateral line, and it's full of omega-3s. And when you cook fresh salmon or open up a can (it's already been cooked), you'll see some grey parts. That's also fat -- the layer right next to the skin. Eat it. Don't cut it away. As for the skin, that's your call. It's also fat, hence omega-3s and pollutants, but too slimy for my personal tastes.

If you buy canned salmon, however, make sure you pick up containers that don't contain the chemical Bisphenol-A. For many years, BPA was used as a glue to keep cans together. Unfortunately, it's also been linked to cancer. Many companies have responded to consumer pressure and stopped using it, but some well-known brands still do. Here's a handy shopping list.

This piece is summary of several posts from Harriet Sugar-Miller's blog.

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