600 Capitol Way North, Olympia, WA 98501-1091

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July 01, 1999
Contact: Madonna Luers, (509) 456-4073

More trout might be possible with in-stream incubators

SPOKANE—It's been done with salmon, so it might be possible with trout – hatching fish eggs right into fishing waters with incubating buckets.

The Washington Department of Fish and Wildlife (WDFW) is experimenting with this idea in northeast Washington in cooperation with the Stevens County Conservation District with funding from Avista Corp., Boise Cascade Corp., and Ponderay Newsprint Co.

Earlier this month, the first "remote site incubators" (RSIs) were placed at the inlet stream to Graham Lake near Colville and, for a more controlled environment, at the Colville Fish Hatchery. The RSIs are five gallon buckets fitted with pipes that allow water to flow over fish eggs on gravel, then upward and out the top, simulating stream conditions. Rainbow trout eggs were placed in the RSIs in densities of 10,000, 5,000, and 1,000 to see which are most successful. After the eggs hatch and the yolk-sac fry grow a little, they should theoretically swim up and out of the RSIs right into their adult habitat.

The process has been successful in western Washington with chum salmon, which lend themselves to the technique because they quickly migrate out of the streams in which they hatch. But the much smaller eggs of trout species, many of which spend most of their lives in the same water where they hatch, may have very different results.

To measure those results, Steven Schroder, an Olympia WDFW fish research scientist, coordinated a special marking of the RSI fish eggs at the Colville Hatchery. Changes in water temperature, even at egg stage, create visible rings on a calcified part of a fish's inner ear, called an "otolith." The rings, similar to computer bar codes used in grocery stores, can be read when otoliths are retrieved from the heads of harvested fish. By changing the temperature of the water in which the eggs were kept each day, Schroder marked the fish in different ring patterns to distinguish the different densities and locations of the RSIs.

Fish otoliths will be collected through angler checks over the next three years to determine if RSI-hatched trout are in the fishery and if they are bigger or fatter than hatchery-raised trout.