Few hatchery brook trout genes found in wild fish

Wild brook trout in the Loyalsock Creek watershed show few genes from hatchery fish, despite many years of the introduction of the stocked trout into those streams, according to a Penn State University study.

Shannon White, a doctoral student and the lead researcher in the study, said the finding is important because it uncovers the potential effects on wild trout populations from hatchery-raised fish.

“This was the first study that we are aware of that looked at genetic introgression on wild brook trout in an actively stocked watershed,” she said. “We were somewhat surprised to find more than nine of the 10 fish we evaluated had the wild trout genotype, because similar studies of wild salmon, rainbow trout and other salmonoids have shown significant genetic introgression from stocked fish.”

Dave Rothrock, of Jersey Shore, said he agreed with the research, but would like to see a more extensive study that reveals the overall impact of stocked brook trout on native populations.

Rothrock, an avid and longtime flyfisherman and local angling guide, said it’s highly likely that the mere introduction of hatchery fish into streams of native populations has an overall negative impact on the wild brook trout.

There are so many factors to consider, including competition between wild and hatchery fish for food and space, and the potential inability of stocked trout to adapt to their new environment.

“When you talk about brook trout, you are talking about a species that is very sensitive,” he said.

The Penn State study considered the introgression in wild brook trout at 30 sites in the watershed.

“Why brook trout aren’t showing high rates of introgression is still uncertain; however, our guess at this point is that it stems from the high mortality of hatchery-raised fish,” White said. “Studies have shown that hatchery-raised fish have low fitness and survival and most die within a few months of stocking due to angler harvest, predation or environmental factors. They are stocked in April and May and most are gone by July, so few make it to the October-November spawning season.”

White noted that hatchery fish simply have a difficult time surviving in small stream eco-systems.

Rothrock agreed that hatchery trout normally do not survive in streams for a full season, but he noted that wild brook trout have life spans of between four and five years.

Wild brook trout are known, he said, to spawn as early as the late summer and into the fall months.

But it’s unclear if hatchery trout readily adapt to that spawning schedule after being introduced to their new environments.

“There were a lot of things that were not addressed in this study,” he said.

In a perfect world, wild trout would be left alone to thrive in their own natural environment without the invasion of hatchery-raised fish.

But that simply is not going to happen, Rothrock agreed, given angler demand for fishing in streams heavily stocked with trout.

“The (state) Fish and Boat Commission has not done anything to educate the population on the value of wild trout,” he said.

Walt Nicholson, president of the Susquehanna Chapter of Trout Unlimited, said hstchery trout are put into streams for the sole purpose of being caught by anglers.

He noted that the stocked brook trout are simply a different fish than the wild species≥

“I think there has always been a misconception that those stocked fish will help sustain wild brook trout,” he said.

Nicholson said the study probably should not be used to conclude that the genetic introgression on wild brook trout by hatchery trout is the same in all watersheds.

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