MILO – Nearly 50,000 young Atlantic salmon were released into a Penobscot River tributary this week as part of a test to see whether new technology will help save the endangered fish.

MariCal Inc., a Portland biotechnology company, has developed a fish-raising process that helps commercial salmon farms improve the growth and survival rates of their pen-raised fish. The company now is applying that technology, which involves manipulating environmental conditions to stimulate the fishes’ proteins, to see if it works on wild Atlantic salmon.

The 7-inch fish released by MariCal officials and federal fisheries agents Tuesday in Milo will swim into the Penobscot and ultimately the Atlantic Ocean. Two years from now, researchers will determine whether the fish return to the river in significant numbers.

“We don’t know how this technology will work because it’s never been used before” on fish in the wild, said Fred Trasko, manager of the Green Lake National Fish Hatchery in Ellsworth. “We’re trying to partner with any research we can find out there that may have applications for saving salmon in the United States.

Maine rivers were once abundant with wild Atlantic salmon. But the stocks dwindled and the federal government in 2000 listed salmon as endangered in eight Maine rivers. In hopes of restoring the populations, federal hatcheries in Maine breed salmon from some of those rivers and release young fish that are old enough to begin the migration to the ocean.

Those restocking efforts, however, have a high rate of failure. Only one-half of 1 percent of the fish released actually return to their native rivers to lay eggs two years later, said John Kocik, a research biologist with the National Marine Fisheries Service.

One explanation for the declining survival rate is that acid rain changes the chemistry of the rivers where the fish are born and makes them less able to adjust to the salt water in the ocean. That’s where MariCal’s technology may help.

The company has identified proteins in fish that regulate growth and other biological processes, including the physical changes that allow a young salmon, or smolt, to survive as it swims into the salty ocean. MariCal researchers also have identified factors such as lighting, water temperatures and feed that can stimulate the proteins.

MariCal uses the process to increase survival rates at salmon farms and believes it also will work on fish being released into the wild. The company received a $40,000 contract to prepare 24,600 1-year-old fish for release by manipulating their environmental conditions for the past five weeks. The company also will test and analyze the fish that are captured when they return in two years to spawn.