Salmon Born in Hatcheries Are Different at DNA Level Than Wild Salmon in Hundreds of Ways

Salmon release
Salmon from a California hatchery are released into the Sacramento River. New research has found that hatchery-born salmon differ from wild salmon in hundreds of ways. Robert Galbraith/Reuters

Seventy percent of salmon at the fish counter grow up in underwater pens packed to the gills. These farmed fish tend to be considered higher in contaminants and unhealthy fats than wild salmon caught in their native habitat.

The bigger problem, though, is that in places like British Columbia, there has been an explosion of these fish farms located out on the sea, contained only by open nets—and that diseases can spread easily from the farmed fish to their wild cousins. Conservationists worry that these diseases could finish off wild salmon populations already decimated by centuries-old land use actions, such as the damming of rivers along the West Coast.

Replenishing wild salmon populations in Oregon and Washington for recreation and agriculture depends on fish bred and born in hatcheries and then released into the wild to come of age and reproduce. But scientists have also long known that salmon born in captivity have a harder time producing offspring once released in the wild than do indigenous wild fish. A 2011 Oregon State University study found that fish born in hatcheries become domesticated in as little as a generation. Adapting to captivity so quickly affects their ability to successfully reproduce in the wild, the study’s lead researcher Michael Blouin reasoned.

For his latest study, published February 17 in the journal Nature Communications, Blouin’s team compared the genes of steelhead trout (a type of salmon) born in hatcheries to hatchery-born parents to those of wild-origin steelheads collected from Oregon’s Hood River. They found differences in more than 700 genes of the hatchery-born fish.

“This pretty much settles the question of whether hatchery fish can be genetically different after just a single generation of domestication,” Blouin says. “What is important is that this work is a step towards trying to figure out which traits are under strong selection in the hatchery, and what hatchery conditions exacerbate that selection.”

In the wild, steelhead trout are solitary and defensive about their turf, but in hatcheries they tend to be packed in like sardines. It’s easy to guess why, over just a generation, the fish developed things like improved immune function—such as wound repair—in this kind of environment. “We don’t yet have data to conclude it’s true,” says Blouin, “but we hypothesize that the wounding that occurs when fish are crowded together and bite each other might cause selection for enhanced wound-repair abilities.”

There’s no direct evidence that hatchery fish are a risk to Oregon’s wild salmon populations, but there is general concern that when hatchery-born fish mate in the wild they might drag down the health of the wild populations. A near consensus exists, however, that the West Coast would be better off with more wild salmon for harvest and recreation. Figuring out how to produce hatchery fish that are more like wild fish could go a long way towards those recovery efforts.

“Once we understand what traits of the fish are being favored in hatcheries, it may be possible to change the way hatchery fish are raised to reduce the selection pressures on them,” Blouin says. “Then one could create hatchery fish that are more like wild fish, thus producing fish for harvest while reducing risk to wild populations.”