A recently published study says that in just one generation traits are selected that allow fish to survive and prosper in the hatchery environment.
“We expected to see some of these changes after multiple generations,” said Mark Christie, an OSU post-doctoral research associate and lead author on the study. “To see these changes happen in a single generation was amazing. Evolutionary change doesn’t always take thousands of years.”
The findings, published last week in Proceedings of the National Academy of Sciences, show a speed of evolution and natural selection that surprised researchers.
“We’ve known for some time that hatchery-born fish are less successful at survival and reproduction in the wild,” said Michael Blouin, a professor of zoology at Oregon State University. “However, until now, it wasn’t clear why. What this study shows is that intense evolutionary pressures in the hatchery rapidly select for fish that excel there, at the expense of their reproductive success in the wild.”
These findings were based on a 19-year genetic analysis of steelhead in Oregon’s Hood River. It examined why hatchery fish struggle to reproduce in wild river conditions. Some of the possible causes explored were environmental effects of captive rearing, inbreeding among close relatives, and unintentional “domestication selection,” or the ability of some fish to adapt to the unique hatchery environment.
The study confirmed that domestication selection was at work.
“It remains to be seen whether results from this one study on steelhead generalize to other hatcheries or salmon species,” Blouin said.
“Nevertheless, this shows that hatcheries can produce fish that are genetically different from wild fish, and that it can happen extraordinarily fast,” he said. “The challenge now is to identify the traits under selection to see if we can slow that rate of domestication.”
It’s not clear exactly what traits are being selected for among the thousands of smolts born in hatcheries, the scientists said, but one of the leading candidates is the ability to tolerate extreme crowding. If research can determine exactly what aspect of hatchery operations is selecting for fish with less fitness in the wild, it could be possible to make changes that would help address the problem, they said.