Feed is indeed the critical link in reducing PCBs in farmed salmon. Salmon farmers recognize this fact and have, in fact, been working for many years to formulate the feeds that have reduced PCB levels in salmon to the low levels of todayon average 1/100 of the FDA tolerance.
Salmon are carnivoresmeat eaters. In the wild, they eat between 10 and 20 pounds of shrimp, krill and small fish to put on a pound of weight. Farmed salmon are also fed a diet that consists partly of fishmeal and oil, and because they don't burn up a lot of energy looking for their next meal, it takes a lot less for a pound of gaingenerally 3-4 pounds of fish based feed and overall about 1.5 pounds of feed. In fish farming about 95% of the biomass grown is harvested.
When salmon were first farmed the diets were primarily all fishmeal and oila natural diet, so to speak. Ten years ago this fell to about 80 percent as other feed sources were substituted. Today, on average, fishmeal and oil comprise about half of the diet. Vegetable meal and oil are finding their way into feeds steadily and surely. These feed components, virtually free of PCBs, and offering salmon farmers an alternate and plentiful source of feed get lots of attention. But, it's not an easy switch. There are multiple issues that have to be solved: palatability (meat eaters don't always like a lot of veggies), nutrition issues, keeping omega-3 fatty acid levels up, and more.
There are dozens of research projects and tens of millions of dollars spent by the industry on this each year. As with feeds and feeding research and development for all speciesland or waterone of the biggest obstacles to change is simply time. Each step, each change in the diet, has to be tested in the real world to see if it works and if it does, fine tuned. While some things, such as palatability, can be tested quickly, other things, such as rate of gain or maintenance of nutritional characteristics, take a lot longera year or more of feeding trials. And many things have to wait for something else to be solved before they can be started on.
Our young industry has made remarkable strides in feeding salmon over the past 10 years. It's one reason PCB levels are so low. It's also one of the reasons desirable omega-3 fatty acids are so high. And it's a big part of why farmed salmon is so affordable. There is a lot of work underway and progress on all fronts will come. Stay tuned.
Source: Salmon Of The Americas - May 2004.