PULLMAN, Wash .– Changes in the epigenetic programming of hatchery-reared rainbow trout could explain their reduced fertility, abnormal health and lower survival rates than wild fish, according to a new study from the University of Washington State.
The study, published May 18 in Environmental Epigenetics, links feeding practices that promote faster growth, as well as other environmental factors in fish hatcheries, and epigenetic changes found in sperm and the red blood cells of the rainbow trout.
The research was carried out at a national hatchery on the Methow River in Winthrop, Washington and at another nearby hatchery on the Colombia River. This could have broader implications, as hatchery-reared rainbow trout breed with wild rainbow trout after being released.
âAlthough they are genetically very similar, rainbow trout raised in hatchery conditions do not have the same level of health and survival as wild-raised fish,â said Michael Skinner, co-author of the study and professor at the WSU School of Biological Sciences. “This research provides a molecular explanation of why we are seeing these differences.”
Skinner is an expert in the field of epigenetics, which is the study of molecular factors and processes around DNA that regulate genome activity independent of DNA sequence.
Although exposure to environmental conditions generally does not affect an organism’s genetic code, previous research has shown that a range of factors, including toxics, stress, and nutrition, can alter the phenotype of an organism. variety of species through epigenetics.
In the present study, Skinner and his colleagues performed molecular analysis of sperm and red blood cells collected both from rainbow trout reared at two Washington fish hatcheries and from trout that have spent their entire lives. in nature.
Although there were negligible genetic differences between the two fish populations, the researchers identified a set of epigenetic features, called DNA methylation regions, in the sperm and red blood cells of rainbow trout. – hatchery-raised skies that were not present in their wild counterparts. .
Skinner’s study connects the dots to identify a molecular mechanism that may help explain many of the physiological differences scientists have noted between hatchery-raised fish and wild fish.
For example, it has been shown that the offspring of fish living even a single generation of hatchery breeding can have diminished fitness, age changes at spawning, altered morphologies and poorly adapted anti-predator behavior. .
In fact, hatchery culture has been shown to reduce the reproductive success of rainbow trout by up to 40% in the first two generations after the fish return to their natural environment.
Another important aspect of the epigenetic alterations identified by Skinner is that they can be transmitted via sperm to subsequent generations.
In places like the Methow and Columbia rivers, where hatchery-reared trout are frequently released and reared with wild trout, epigenetic inheritance could already have had a substantial impact on the overall health and fitness of the fish population. , Skinner said.
“We believe that the large number of hatchery fish that have been released and reared with the wild fish population of the Methow River over the past 60 years has had a significant influence on the health of the overall population,” a- he declared. âGoing forward, our research suggests that hatchery operations should consider not allowing crosses with wild fish populations. Otherwise, the impacts on wild farmed rainbow trout and the environment could be dramatic and alter the future trajectory of the overall population.