Study identifies rapid genetic changes in salmon hatcheries

Researchers at Oregon State University (OSU) have found that the offspring of wild salmon and first-generation hatchery fish differed in the activity of more than 700 genes.

The study on steelhead trout, a collaborative project between OSU and the Oregon Department of Fisheries and Wildlife, in the northwestern United States, offers genetic evidence that wild and hatchery fish are different at the DNA level.

In a paper published in Nature Communications, researchers said the wild and hatchery fish can become different with surprising speed, and a single generation of adaptation to the hatchery resulted in observable DNA changes that were passed on to offspring.

"A fish hatchery is a very artificial environment that causes strong natural selection pressures," said Michael Blouin, a professor of integrative biology in the OSU College of Science. "A concrete box with 50,000 other fish all crowded together and fed pellet food is clearly a lot different than an open stream."

Aside from crowding, which is common in the hatchery, injuries also happen more often and disease can be more prevalent.

Mark Christie, lead author of the study, said "a large number of genes were involved in pathways related to wound healing, immunity, and metabolism, and this is consistent with the idea that the earliest stages of domestication may involve adapting to highly crowded conditions."

The genetic changes are substantial and rapid, the study found. It is literally a process of evolution at work, but in this case it does not take multiple generations or long periods of time. "We expected hatcheries to have a genetic impact," Blouin said. "However, the large amount of change we observed at the DNA level was really amazing."

Differences in survival and reproductive success between hatchery and wild fish have long offered evidence of rapid adaptation to the hatchery environment. The new DNA evidence directly measured the activity of all genes in the offspring of hatchery and wild fish. It conclusively demonstrates that the genetic differences between hatchery and wild fish are large in scale and fully heritable.

While the study was able to identify some genetic changes that may explain how the fish are responding to the novel environment in the hatchery, researchers acknowledge that they do not know exactly what traits are being selected for.

With the question put to rest of whether hatchery fish are different, Blouin said, it may now be possible to determine how they are different, and work to address that problem. When the genetic changes that occur in a hatchery environment are better understood, it could be possible to change the way fish are raised in order to produce hatchery fish that are more like wild fish. Endit