Although paddlefish restoration efforts have been a bit of an upstream paddle, state biologists are determined to repopulate Western Pennsylvania waterways with the ancient, native species.

On Wednesday, fish culturists from the Pennsylvania Fish and Boat Commission's Linesville hatchery will plant fingerlings in the Ohio River, in the 17th year of the agency's paddlefish plan.

"Paddlefish belong there. They're part of the ecological realm," said commission biologist Rick Lorson. "We equate it to managing for striped bass in the Susquehanna and Delaware and shad in the Susquehanna. All are native to their river systems."

The fish in Wednesday's planting will be larger than in the past, and there will be more of them in the hope it will bolster their chances of survival, given predation by muskies and walleyes.

Adults stocked years ago have been landed by anglers targeting other species, and scientists have captured paddlefish in surveys. But they have never netted a juvenile, and an effort in 2006 to cull young fish from likely nursery waters -- the ultimate measure of the program's success -- was unproductive.

"We know paddlefish are going through the spawning motions," said Lorson. "But are they reproducing? We just don't know."

Although young paddlefish grow quickly, Lorson said it takes about 10 years for them to become sexually mature. Not all of them spawn annually, which helps explain why their roe -- a type of caviar -- can sell for $100 a pound in states where harvesting the species is legal.

In Pennsylvania, paddlefish are considered "extirpated." Anglers must return them unharmed to the water immediately.

"Conditions have to be right for them to spawn," Lorson said. "We need flood-like flow -- water about six feet above normal -- for paddlefish to move to suitable spawning grounds."

Paddlefish can easily travel 100 miles to reproduce in late May, but have been known to go 10 times farther to find the gravelly spawning habitat they need, using their long rostrums, or beaks, for balance in strong current. They can spawn in more confined areas, too, Lorson said, if suitable habitat and enough plankton -- their sole food source -- is available. Plankton densities in the Ohio River near Pittsburgh are low compared with more southerly portions of the same waterway where wild paddlefish are known to exist. Paddlefish also thrive in the Midwest, where it is legal in some states to snag them for sport.

Paddlefish disappeared from Pennsylvania almost a century ago as a consequence of water pollution, the installation of locks and dams and sand and gravel dredging. The last historical account of a paddlefish in Pennsylvania was in 1919 at the mouth of the Kiskiminetas River on the Allegheny.

While dams and dredging remain a threat, Lorson said, water quality has improved enough to warrant paddlefish plantings, and to encourage populations from neighboring states to expand to western Pennsylvania.

"With reductions in acid mine drainage, industrial pollution and sewage, we thought conditions would be right to try to restore this native fish," Lorson said.

New York and West Virginia have launched similar efforts on the Allegheny and Ohio rivers, respectively. Within the past two months, the commission has documented three New York-tagged paddlefish below the Kinzua Dam, and Shane Hennessy of Allegheny Field and Stream, a Warren, Pa., tackle shop, said anglers released four paddlefish this year, including one over 30 pounds.

"We're hearing more and more about paddlefish from guys fishing," Hennessy said.

Lorson finds that encouraging.

"It's an indication we have adult fish out there," he said. "We're closing in from three directions."

Still, he is eager to find juvenile fish and to document evidence of natural reproduction, which is the program's goal. Given how slowly paddlefish become reproductively viable, Lorson is committed to a long-term effort.

He is seeking additional funding from the U.S. Fish and Wildlife Service, the commission's partner in the stocking program, to perform fine-mesh net sampling every five years.

"Our goal is to take paddlefish from extirpated to endangered," he said. "We're working hard to make that happen."

Anglers who catch paddlefish in Pennsylvania are urged to take a photo, if possible, before releasing the fish and to contact the Fish and Boat Commission.