Farm-raised or wild-caught? That’s a question many people have asked themselves when it comes to buying salmon for dinner. Experts are now concerned about wild and farm-raised salmon associating with one another.
Each year, millions of salmon escape fish farms and reenter waterways, where they are reunited with their wild brethren. On the surface, that may not seem problematic – after all, salmon are salmon. But as it turns out, that’s not exactly the case.
There are genetic differences; farm-raised salmon, for instance, are more aggressive and have less natural ability to evade predators. The fear is that these millions of escapee salmon could breed with wild fish, passing on their inferior genes and weakening local populations. This has led some experts to advocate for the sterilization of farm-raised salmon.
New research shows that although farm-raised fish are inferior to their wild counterparts at spawning, their sperm and eggs are equally potent. And there is some evidence that crossbreeding is already underway. In Norway, where farmed fish make up 50 percent of the salmon in some rivers, populations have shown genetic changes that point to hybridization.
The proposed sterilization would be done by pressure-treating salmon eggs after fertilization. This creates a condition called “triploidy,” in which the salmon would grow normally but possess both sex chromosomes, which generally makes them infertile. Although the process is already common with rainbow trout, the salmon industry thus far has not embraced it.
One thing is clear: wild salmon – whose numbers are a mere one-tenth of what they were 50 years ago – need protection.
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Web Links
Time to sterilise farmed salmon to save wild cousins
Sterilise farmed salmon to stop breeding with wild fish, researchers say
Photo, taken December 26, 2011, courtesy of Jude Adamson via Flickr.
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Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.