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Farmed salmon more successful breeders

2nd June 2003

Biological Research Information Center

Young male salmon that grew up on the farm may have better success in mating than their wild cousins, according to an aquarium study. The farmed fishes' knack for breeding may prove to be an unexpected threat to the integrity of wild salmon stocks.
Scientists worry that escapees from salmon farms may push wild salmon out of existence by competing for food, for example, or interbreeding.

Aquaculturists dismiss those concerns, arguing that farmed fish are less likely to survive in the wild, let alone live long enough to mature and mate. Some researchers were especially concerned about a life-stage of salmon, called a parr, which matures early in the safer confines of freshwater streams, before heading out to sea. And young farmed parr, researchers have now shown, could be ready and waiting when wild female salmon come inland to spawn.

The team bred wild salmon with both wild and farmed parr in tanks designed to simulate a stream environment. After testing the fertilized eggs, they found that the farmed parr had fertilized almost four times as many eggs as the wild parr did (and just less than twice as many as the hybrid parr). That could be because farmed parr tend to be "more aggressive to some extent, and more risk prone," says Dany Garant of the University of Oxford, U.K., an author on the paper published in the June issue of Ecology Letters. The young farmed males, he speculates, may be less wary of predators compared to wild fish, which seem to be more skittish and take a little longer to return to a nest. Even though the authors haven't yet assessed the actual genetic contribution of farmed parr in the wild, Garant says it's likely to be more than expected, especially when magnified by generations of spawning. The authors point out that the shorter breeding generations of farmed parr could also accelerate the loss of the wild genotype.

"This paper shows that the escapees from farmed salmon are disproportionately represented" in breeding, says John Volpe of the University of Alberta in Edmonton. "Nobody before has empirically tested that.” Bill Muir, a fish geneticist at Purdue University in West Lafayette, Indiana, is also impressed with the work. "This certainly provides a new avenue that people hadn't thought of before" for spreading domesticated fish genes into wild populations more quickly in fewer generations, he says.

Naomi Lubick