Epigenetics examine attracts hyperlink between hatchery circumstances and steelhead trout health

Michael Skinner in his laboratory at WSU. Photo credit: WSU

Changes in the epigenetic programming of hatchery-reared steelhead trout could be responsible for their decreased fertility, abnormal health, and lower survival rates compared to wild fish, according to a new study from Washington State University.

The study, published May 18 in Environmental Epigenetics, links feeding practices that promote faster growth and other environmental factors in hatcheries to epigenetic changes in the sperm and red blood cells of steelhead trout.

The research was conducted at a national fish hatchery on the Methow River in Winthrop, Washington, and another hatchery nearby on the Colombia River. This could have more far-reaching effects, as steelheads raised in the hatchery multiply with wild steelheads once they are released.

“Although steelhead trout are very similar genetically, they do not have the same health status and survivability under hatching conditions as wild-farmed fish,” said Michael Skinner, co-author and professor at the WSU School of Biological Sciences. “This research provides a molecular explanation for why we see these differences.”

Skinner is an expert in the field of epigenetics, which studies molecular factors and processes surrounding DNA that regulate genome activity regardless of DNA sequence.

While exposure to environmental conditions does not typically affect an organism’s genetic code, previous research has shown that a number of factors, including toxins, stress, and diet, can develop the phenotype of a wide variety of species through epigenetics.

In the current study, Skinner and colleagues performed a molecular analysis of sperm and red blood cells obtained from steelhead trout raised in two fish hatcheries in Washington as well as trout that have lived in the wild all their lives.

While there were negligible genetic differences between the two fish populations, the researchers identified a number of epigenetic traits, known as regions of DNA methylation, in the sperm and red blood cells of the brooding steelhead that were not present in their wildly bred counterparts.

Skinner’s study ties the dots together to identify a molecular mechanism that may explain many of the physiological differences that scientists have found between hatching and wild fish.

For example, it has been shown that the offspring of fish that have undergone a single generation of brood rearing themselves may exhibit decreased fitness, age changes at spawning, altered morphologies, and poorly adapted anti-predator behavior.

In fact, brood rearing has been shown to reduce the reproductive success of steelhead trout by up to 40% in the first two generations after the fish have been returned to their natural environment.

Another important aspect of the epigenetic changes identified by Skinner is that they can be passed on to subsequent generations via the sperm.

In places like the Methow and Columbia Rivers, where brood trout are widely released and reared with wild trout, epigenetic inheritance could already have had a significant impact on the overall health and fitness of the fish population, Skinner said.

“We believe the large numbers of hatchery fish that have been released and reared with the Methow River wild fish population over the past 60 years have had a significant impact on the health of the overall population,” he said. “Our research suggests that hatcheries should consider avoiding crossbreeding with wild fish populations. If not, the effects on wild-farmed steelhead trout and the environment could be dramatic and change future population trends.”

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More information:
Environmental Epigenetics, DOI: 10.1093 / eep / dvab002 Provided by Washington State University

Quote: The epigenetic study establishes a link between breeding conditions and the fitness of steelhead trout (2021, May 18), published on May 18, 2021 from https://phys.org/news/2021-05-epigenetics-link -hatchery-conditions-steelhead.html was obtained

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