Fishy fear of the known.

Fishy fear of the known

Courage and innocence, the poets tell us, are admirabletraits. But in some cases it's much wiser just to turn tail and run--or, as research at the Oregon State University Hatfield Marine Science Center in Newport shows, to turn fin and swim.

Fish hatcheries in the Pacific Northwest and throughout theworld release millions of young salmon every year, but typically only about 5 percent survive the hostile ocean environment and return to their freshwater spawning grounds. And that figure can inexplicably fluctuate from year to year.

In an unusual laboratory with fish tanks inside fish tanks,Oregon State professor and National Marine Fisheries Service scientist Bori Olla is trying to instill in salmon the fear of cod, a natural predator of the commercially valuable salmon. He is teaching the "naive" hatchery salmon a lesson in life by either putting them in a tank surrounded by transparent Plexiglas with hungry cod hitting the other side of the walls, or else dropping dead, frozen cod in their midst.

According to Olla, who says salmon learn very quickly, themost "startling" results thus far are those showing varying vulnerability in individual fish to very subtle stresses affecting the likelihood of surviving an attack. Olla thinks that hatchery fish--unthreatened by the humdrum safety of their tanks -- may be taught prophylactic cowardice through measures as simple as periodically disturbing the water's surface or dropping in artificial predators.

"Salmon have evolved mechanisms of recognizing predatorsand live prey," he told SCIENCE NEWS. "We're awakening a memory." Olla says preliminary laboratory results have shown some "very dramatic differences" in salmon survival, suggesting that commercial hatcheries might adopt some scale-raising techniques of their own.