OSU post-doctoral researcher Mark Christie was amazed at the changes. (Photo: oregonstate.edu)
Hatchery-raised fish less fruitful in the wild: study
Wednesday, December 21, 2011, 15:40 (GMT + 9)
A study has found that in just one generation salmonid traits are selected allowing the fish to survive and thrive in the hatchery environment. However, this compromises the salmon’s ability to spawn in the wild, meaning that hatchery-raised fish may not be able to help increase wild stocks.
The findings, published this week in Proceedings of the National Academy of Sciences, confirmed that it is a change in fish genetics not a temporary environmental effect; it is a primary impact of hatcheries.
“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,” he stated.
This and other studies continue to note concerns regarding the genetic impacts that hatchery fish may have when they interbreed with wild salmon and steelhead and whether they will help replenish wild salmonid stocks.
This study used a 19-year genetic analysis of steelhead in Oregon’s Hood River to analyse 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” – the latter of which was confirmed to be occurring.
When thousands of smolts are born in the artificial environment of a hatchery, those that prosper are the ones that can handle hatchery conditions. But these same traits can backfire in the wild, as their ability to produce surviving offspring is much reduced.
“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.”
One of the dominating traits is the ability to tolerate extreme crowding. Scientists said that if they can determine exactly what aspect of hatchery operations is selecting for fish with less fitness in the wild, it could be possible to help address the problem.
Billions of captive-reared salmon are released into the wild each year to boost fishery yields and populations. The recovery plan of steelhead studied in this research, which are listed as threatened under the Endangered Species Act, includes supplementation with hatchery fish.
“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.”
By Natalia Real