YOUNG male salmon raised in fish farms mate more aggressively than their counterparts in the wild. This means that fish escaping from farms are likely to pose a greater threat to native species than previously thought, by depleting wild fish populations and reducing their genetic diversity.
Farmed salmon are bred to grow rapidly in crowded conditions, and this makes them more aggressive than wild fish. Environmentalists have been concerned that fish escaping from farms are displacing wild salmon from their natural habitats, but such fears have been tempered by findings that adult escapees are less successful than native fish at reproducing in the wild.
However, salmon have an alternative reproductive strategy, in which some male yearlings, known as parr, mature early and mate. These tiny fish can sneak past full-grown males up to 10 times their length and fertilise more than a third of the eggs in a female's nest. ...
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