By JOHN O'CONNELL
Researchers with the University of Idaho and the U.S. Geological Survey partnered to develop a test using DNA left behind in water to detect early infestations of invasive New Zealand mud snails.
The test should provide a cheaper and more effective tool for fish hatcheries that move brood into untainted waters, said Adam Sepulveda, aquatic ecologist with the USGS Northern Rockies Research Station in Bozeman, Mont.
The research was published online in mid-June in the journal Freshwater Science and should come out in print soon.
The asexual mollusks are about the size of a sesame seed and multiply quickly, outcompeting native species. They're low in nutrition and can lead to smaller salmon and other fish that fill up on them rather than better food sources. They also disrupt the balance of carbon and nitrogen in streams.
"For invasive species, we really want to catch them long, long before they get to the point of being obvious," said Caren Goldberg, a research scientist with U of I's fish and wildlife department, who led the research project.
The current test involves disturbing rocks in streams, collecting insects that surface and studying samples for invertebrates. Sepulveda said it's akin to seeking a needle in a haystack when just a few mud snails are present, and it costs about $300 to analyze each sample, roughly 10 times the method devised by U of I and USGS.
The new test utilizes so-called eDNA, detecting trace amounts of cells shed by mud snails into their environment. Researchers in France first proved in 2008 that eDNA could show the presence of animals in a wetland. In 2011, a U of I team demonstrated it could also work in moving water, where DNA is diluted and washed downstream. For the mud snail research, the scientists took samples from Idaho's Portneuf River and analyzed them using polymerase chain reaction, in which probes with mud snail genetic sequences match up with corresponding genetic material from the sample and are replicated to be more easily detectible.
Sepulveda said ultraviolet light and warm temperatures can degrade eDNA, and researchers are still learning how far downstream from snails detections can be made.
New Zealand mud snails are now spread throughout the world, including in Idaho, Calfiornia, Washington and Oregon.
"There's no good way to get rid of them. What we do at this point is try to limit mechanisms of spread," Sepulveda said.
He expects the Idaho Department of Fish and Game may use the test for its hatcheries, and it could also be useful to private Thousand Springs fish farms that sell trout for stocking.
Randy MacMillan, vice president of research and environmental affairs with Buhl-based Clear Springs Foods, considers eDNA to be "an intriguing tool," and said New Zealand mud snails are abundant throughout the Thousand Springs reach. But his trout farm doesn't routinely test for New Zealand mud snails because its fish are sold commercially rather than moved to other waters.
"It may have some value with risk minimization," MacMillan said. "There are still questions whether you get false positives with that technology."