Genes of hatchery steelhead change in just one generation

It takes just one generation for the DNA of steelhead domesticated in hatcheries to be altered and to be significantly different than steelhead whose parents are wild, according to a recent study by Oregon State University.

In fact the study found that in just one generation there were 723 genes that differed between the offspring of wild steelhead and the offspring of first-generation hatchery steelhead.

Further, the study found through gene enrichment analysis that adapting to the hatchery environment involves responses by the steelhead in wound healing, immunity and metabolism, suggesting the adaptation is due to crowding in hatcheries.

“We found hundreds of genes were   expressed   differently   between the offspring of first-generation hatchery fish and the offspring of wild fish, and that the difference was heritable from their parents,” said lead researcher Michael Blouin, professor in the Department of Integrative Biology at OSU.

Although over 700 genes are just a small fraction of the total number of genes in the genome, Blouin said it is a surprisingly high number to show a difference after just one generation of selection.

The results show that hatchery fish can be genetically different from wild fish after only a generation of selection in a hatchery, he said, and “more importantly, it allows us to generate hypotheses about what types of traits are under selection in hatcheries.”

“For example,” he continued, “the fact that many of the differentially expressed genes are involved in immune-related functions, such as wound repair, suggests the hypothesis that hatchery fish might be selected for their ability to tolerate injuries. This is actually consistent with the idea that crowding is a selective factor, given juvenile steelhead can be pretty aggressive with each other in captivity.”

Blouin cautioned that the hypothesis still needs to be tested, “but data such as these may eventually lead us to the traits under selection, and thus to ideas on how we might want to modify hatchery culture practices.”

According to the study, steelhead are one of the few fish species considered to have been fully domesticated and the responses to selection routinely occur in steelhead within less than ten generations of captive breeding. This is the first study to demonstrate that the earliest stages of domestication are characterized by large changes in heritable patterns of gene expression.

“We hypothesize that adaptation to crowded conditions may drive much of this early domestication. Regardless of the mechanism, it is remarkable that a single generation of domestication can translate into heritable differences in expression at hundreds of genes,” the study says.

This is the second study about crowding in hatcheries and the domestication of hatchery steelhead Blouin and others have published recently. “The effects of high rearing density on the potential for domestication selection in hatchery culture of steelhead. Blouin said the overall goals of the two studies are similar.

“Substantial evidence suggests that salmonid fish rapidly adapt to hatcheries in ways that make them less fit in the wild,” he said. “But we don’t know what traits are under selection in the hatcheries or what environmental conditions of the hatchery cause such strong selection pressures.”

He added that the goal of his research is to answer those two questions – what traits and what conditions – to discover ways to modify hatchery rearing practices in order to reduce the selection pressures, thereby producing hatchery fish that are more like wild fish.

The first study, he said, was to test a hypothesis about how crowding can increase the rate of domestication, while this more recent study looks at DNA level changes after selection “in order to generate hypotheses about what traits might be responding to selection.”

“Our goal here is not to bash hatcheries,” Blouin said. “Our goal is to figure out how to improve them. If one could modify hatchery practices in order to produce hatchery fish that are more like wild fish, then that would reduce concerns about genetic impacts of hatchery fish on wild populations.”

The modification could be as simple as changing the way hatchery fish are fed or housed, or it may be that the goal of making hatchery fish more like wild fish is not feasible. “We won’t know until researchers tackle the question,” Blouin said.

Image: Photo Courtesy ODFW. Steelhead raised in hatcheries can different in hundreds of subtle ways at the genetic level, according to research conducted by a team at Oregon State University.