updated 3/5/2007 9:54:39 PM ET 2007-03-06T02:54:39

With spring approaching, Virginia scientists are planning a more comprehensive attack to find the cause of the mysterious fish kills in the Shenandoah River and its tributaries.

State agencies will continue practices of monitoring water quality and testing fish specimens that they've conducted since thousands of fish began dying for unexplained reasons three years ago.

But based on advice from two university professors, scientists will broaden their search for the cause or causes, state Department of Environmental Quality biologist Don Kain said Monday.

Don Orth, a Virginia Tech professor of fisheries and wildlife science, said he also will solicit help from scientists doing research in the valley that's unrelated to the fish kills.

"There is something wrong systemically with the whole basin," said Orth, who along with Greg Garman of Virginia Commonwealth University helped state scientists focus their fish kill investigation.

For one thing, scientists will look for compounds such as heavy metals and pesticides and other chemicals that could cause the symptoms of chronic stress that the dead fish exhibited. Many of the fish that died had lesions that resembled cigar burns. Some were intersex fish, meaning they had both male and female characteristics.

Previous tests have focused on nutrients such as nitrogen and phosphorous, which Kain said are easy to test for. Researchers now also will look for chemicals that are used specifically in the Shenandoah Valley, a largely agricultural area with the highest concentration of poultry and livestock in the state.

"We're going to the next level," Kain said.

One study to be examined will be a Virginia Tech colleague's research on arsenic's movement through the Shenandoah Valley soil, Orth said. An arsenic compound has been added to chicken feed for years, he said.

For the first time, state officials will use monitoring devices containing a liquid that attracts certain types of compounds. This will be a way to find compounds that might not show up on regular measurements but would show high concentrations over time, Kain said.

Scientists also will pay attention to water quality before, during and after storms to see what changes occur from runoff.

The Shenandoah Valley's geology is unique in that it has a number of cracks and crevices that provide a direct link to the river from inland areas, Orth said.

"That forces us to look beyond the pipes and the near-stream effects," he said.

Fish samples will continue to be analyzed for viruses, bacteria and parasites, but Kain said scientists will look for similarities to fish diseases that have been discovered in other areas.

Fish kills in the Great Lakes were caused by a virus that Virginia scientists hadn't tested for previously, he said. Scientists also want to see whether a virus that's supposed to affect only largemouth bass could be involved.

"Viruses do change over time," Kain said. "They mutate."

No largemouth bass have been affected in the Shenandoah, where smallmouth bass, redbreast sunfish and sucker species have died.

Last spring, northern hogsuckers died on the mainstem Shenandoah River, and smallmouth bass and sunfish died in the North Fork of the Shenandoah and in South River.

In 2005, 80 percent of the smallmouth bass and redbreast sunfish in the South Fork developed lesions and died. The kill was similar to one in 2004 on the North Fork of the Shenandoah.

A kill last December on the main branch of the Shenandoah affected several hundred fish, mostly hogsuckers.

Previous spring fish kills have begun early in March, but Kain said Monday that no dead fish have been found so far this year. Scientists have no idea where kills might occur this year.

"I think the odds are this year we can see a fish kill anywhere," Orth said.

Copyright 2007 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.


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