What happens when we feed fish like a cow?

Joe Scharcz, The Gazette 8 Mar 08;

It's a strange world. Health food stores promote dietary supplements of astaxanthin, claiming more powerful antioxidant benefits than with either vitamin E or beta-carotene. It helps protect against the damaging effects of pollution, ultraviolet light and immune stress, they say.

But California's Supreme Court has ruled private citizens can sue stores if they sell fish without declaring that astaxanthin has been added to their feed. What's going on?

Astaxanthin is a naturally occurring pigment found in a variety of algae that serve as food for krill, shrimp and crayfish, imparting an orange-yellow colour to these creatures.

Algae produce astaxanthin for the same reason that many plant and animal species produce such antioxidants. They mop up the potentially harmful free radicals that are the byproducts of metabolism and also offer protection from the damage that can be caused by ultraviolet light.

This protection is transferred to the algae's predators, and then to the predators of those predators. Which explains why wild salmon develop their classic orange colour.

These days, however, most salmon are raised on fish farms. No, they're not genetically modified mutants that graze on the prairies, they are fish raised in penned-off areas of the ocean, where instead of having to search for fresh krill, they can just lounge around waiting to be served a commercially concocted feast.

But these pellets, made from fish too small and bony to be used for human consumption, lack the astaxanthin that gives wild salmon its classic colour. Without astaxanthin, the flesh of farmed salmon turns out to be an unappetizing grey.

And more grey means less green in the cash register. So the answer is to add astaxanthin to the feed.

The commercial production of astaxanthin is a huge industry, relying on three distinct processes. Fermentation of sugar by certain yeasts can produce the compound, as can extraction from specially grown algae.

But the most economical, and therefore the most common process, relies on a 14-step chemical synthesis from raw materials sourced from petroleum. Actually, the name astaxanthin refers to any one of three very closely related compounds with very subtle differences in molecular structure.

The ratio of the three produced by any of the commercial processes is the same, but differs from the ratio found in wild salmon. A technique known as high performance liquid chromatography (HPLC) can be used to separate and quantify the three "stereoisomers" of astaxanthin, and hence determine whether the sample came from wild or farmed salmon.

Why should anyone care about this?

Because wild salmon is prized more by consumers than farmed salmon! Some claim that they prefer the taste, but most who care about the origin of their salmon are concerned about their health.

They've heard of studies showing that farmed salmon are higher in toxins such as PCBs than the wild variety. This may well be the case, since the meal fed to farmed salmon is made from fish often caught in more polluted areas of the ocean than where wild salmon feed.

Whether these trace amounts of PCBs are of any health significance is debatable. My guess is that they are not.

But what is beyond debate, is that wild salmon fetch a higher price. So selling farmed salmon as wild is a lucrative, but obviously unethical proposition.