Scientists have long theorized the differences between wild and hatchery-born salmons, but a new study offers genetic evidence that both groups of fish have various characteristics that set them apart from one another.

Furthermore, the speed of the hatchery-born salmon's adaptation is quite surprising. These species can evolve within one generation and change drastically from their wild counterparts.

Settling the Discussion

Working with specialists from Oregon's Fisheries and Wildlife department, a group of experts from Oregon State University specifically examined the steelhead trout salmon.

Researchers have discovered approximately 736 genetic differences between salmon raised in hatchery and salmon found in the wild. These changes in DNA were passed on to offspring.

The differences in reproduction and survival between species of wild salmon and hatchery-born salmon have long indicated the swift adaptation of the latter to its confined environments.

For instance, when hatchery-born salmon are released into the wild, they find it harder to reproduce compared to their native cousins.

"We observed that a large number of genes were involved in pathways related to wound healing, immunity, and metabolism," said study lead author Mark Christie. He said this matches the idea that earliest stages of salmon domestication may involve adaptation to conditions that are highly-crowded.

The team's findings finally settle the question of whether farm-raised salmon can be genetically different after just a single generation of domestication. Michael Blouin, another author of the study, believes so.

"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," said Blouin.

Saving Depleted Wildlife Population

Bouin, who is also an integrative biology professor in OSU's College of Science, explained that a fish hatchery is an artificial environment that causes strong natural selection pressures.

He said that clearly, a concrete box that hosts 50,000 fish crowded together and fed with pellet food is different than an open stream where fish can swim freely.

Within fish hatcheries, salmon are packed gill-to-gill. They are often contained by open nets, and so the environment can become a breeding ground for contamination and disease.

Most of the commercially-sold salmon are raised in fish hatcheries, and are thought to have higher contaminants than those caught in the wild.

Conservationists are worried that these conditions could cause the spread of disease among the already depleted population of wild salmon. Hatchery-born salmon suffer more from injuries and disease outbreaks.

But the new study provides insight on how to improve artificial fish farms so the salmon they produce are more similar to their cousins in the wild, and ultimately recover the dwindling population.

"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," said Bouin.

Since the genetic changes are rapid, it is clearly due to natural evolution. Scientists said it does not take multiple generations for the adaptations to take effect in the next generations of salmon.

The findings of the study are issued in the journal Nature Communications.

Photo: Oregon State University | Flickr

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