New Evidence that Hatchery Practices Trigger Changes in Steelhead by Altering Gene Expression
Photo courtesy of Copi Vojta
Our Science Advisor Guy Fleischer helps shed light on important new research from Washington State University looking at the biological causes of consequences to steelhead raised in hatcheries.
By Guy Fleischer
A recently published study by leading researchers at Washington State University (WSU) details important new insights into the negative physical effects of raising steelhead in hatcheries. While many of these effects are already known, the study provides additional perspectives on how these changes occur and their corrosive intergenerational impacts when the hatchery fish go on to breed with wild steelhead. The research compared fish raised at hatcheries on the Methow and Columbia Rivers with their wild counterparts.
Dr. Michael Skinner and colleagues at the Center for Reproductive Biology, School of Biological Sciences at WSU found that typical hatchery conditions impose nutritional, behavioral, and other types of stressors on the fish raised in captivity. These influences can developmentally promote altered gene expression in young fish. These types of physical changes to the fish (or any animal) are broadly termed “Epigenetic Programming” and are important for anglers and conservationists to understand.
Epigenetic effects are not genetic mutations. They are alterations in how an animal’s genes are expressed in response to its environment. Epigenetics provides a molecular mechanism for understanding the physiological changes observed in an animal. In the case of steelhead, these hatchery-induced alterations include the decreased fitness of the fish and their subsequent offspring. These changes include shifts in age at spawning, body shape and physical characteristics, abnormal growth rate, brain development, lack of anti-predator behavior, and tendencies for migration, among others.
These results should not be surprising. The artificial setting of a hatchery deprives the young fish of natural conditions that are important for selection for fitness a wild fish would need to survive in the natural environment. There is strong evidence that epigenetic shifts during early life play a significant role in directing the life history and physical or behavioral characteristics of fish during adulthood.
The research also shows that these impacts aren’t limited to the fish directly reared in a hatchery. They might begin there, but they can also be passed to the next generation of offspring when the fish reproduce. Epigenetic inheritance has been shown to influence the next generation’s phenotypes (physical and behavioral characteristics) and health and can be passed onto future generations - even though the fish are genetically identical - in the absence of the original environmental causes.
For example, a steelhead coddled in the hatchery setting could end up with a less-developed brain or manifest in aberrant behaviors than a comparable wild fish of the same age. If the hatchery fish beats the odds and manages to return to spawn, its offspring could inherit a similar brain, and other traits, even though they never lived in the hatchery.
This feature has the potential to dramatically impact the evolutionary-derived fitness of a wild population of fish whenever wild fish are allowed to interbreed with epigenetically altered hatchery fish. Under natural environmental conditions, epigenetic adjustments are a brilliant evolutionary strategy by a mechanism of non-genetic inheritance - it is a powerful way for a parent to pass the best traits for survival along to their offspring - but one that becomes distorted when developed under the unnatural circumstances of artificial propagation.
Basically, epigenetic markers offer evidence of how, and why, hatchery-reared steelhead survive at much lower rates than wild fish. And why the offspring between genetically identical wild steelhead and hatchery steelhead are often far less likely to survive than the fish born from two wild parents. Previous studies have documented that hatchery rearing decreases reproductive success in steelhead by about 40% per captive-reared generation when fish are planted back into natural environments.
Dr. Skinner’s study concludes: “Our research suggests hatchery operations should consider not allowing interbreeding with wild fish populations. If not, impacts on wild-raised steelhead trout and the environment could be dramatic and alter the future trajectory of the overall population.”
These findings add additional evidence and further underline the obligation of fishery managers to consider and take effective steps to monitor and prevent situations where hatchery steelhead populations - which are characterized by reduced fertility, abnormal health, and poor survival compared to wild populations - are intentionally or inadvertently allowed to mix with wild fish in the natural ecosystem.
Additional Resources
WSU News Release: “Hatchery conditions linked to lower steelhead trout survival”