SEATTLE (AP) _ A plan to create a super breed of sexless salmon has been hatched by the state Department of Fisheries, which has released 150,000 of the young coho into Puget Sound.

The experiment is designed to create coho that will ignore the biological urge to spawn and die, thus living longer and growing larger.

Supporters say it could greatly improve sports fishing in Puget Sound by doubling the size of some coho and letting them live two years longer than their typical three years.

But critics have wondered whether tinkering with nature could harm the sound's fragile ecosystem.

''No one knows what could happen,'' says Lee Blankenship, who is in charge of stock identification for state fisheries. ''Will this produce some giant predators that will gobble up fish?''

The fish were sterilized, tagged and released last year from the department's Puyallup hatchery, The Seattle Times reported Wednesday.

A scientist who helped with the sterilization dismissed criticism of the program.

''Let's face it,'' said Sam Milham, of the Department of Social and Health Services. Fisheries officials have ''been fooling around with nature with hatcheries forever. And (the fish) are only going to live another two years. They're not going to get as big as sharks.''

An average coho ranges from eight to 11 pounds.

There is one problem with the program, however.

''We have no idea where they (the salmon) are going to go,'' said Walton Dickoff, a researcher with the University of Washington School of Fisheries.

Since the fish have been stripped of their instinct to spawn, they may swim about aimlessly, remain in Puget Sound or off the Washington coast or travel to Alaska, he said.