Zoology: Outlets for Troutlets

To Biologist Yukitaka Kanayama of Tokyo's Hosei University, the shimmering beauty of live rainbow trout is something to stir the scientific imagination. It pained Kanayama to think that most of the rainbow infants raised in Japan's hatcheries are no sooner released in a river than they are gobbled up by bigger fish, including their own elders. He decided to send rainbow babies to survival school.

Aided by a small grant from Japan's Fisheries Resources Conservation Society, he assembled a classroom for baby trout. In the center of a glass tank 10 in. in diameter, he hung a 3 in. ring of bare wire with six short wires dangling from it. Inside the ring swam a 21-in. "fish" cut from a tin can. The ring and fish were charged with electricity of opposite polarity, thus creating a mild electric field inside the ring.

For Their Own Good. Hatchery-innocent rainbow troutlets, less than an inch long, were plopped into the classroom. With the current turned off, they swam about at random, brushing the wires and the tin fish. But when Kanayama switched on the current, they darted all over the tank, desperate to avoid the harmless but painful shock. "I never felt guilty for doing this," says Kanayama fondly. "It was all for their own good."

Little by little, each class of troutlets learned to stay as far as possible from the tin fish hanging inside the ring. It took about two weeks to train a class so completely that none of them ever risked an electric shock. Then Kanayama held a graduation exercise. He put his pupils in one half of a tank divided by a wire screen through which they could swim easily. On the other side was a grown rainbow trout too big to pass through the screen's meshes. Untutored troutlets wandered guilelessly through the screen and were swallowed by the big fish, but Kanayama's conditioned babies made no such mistake. They associated painful shocks with the tin fish, and they associated the tin fish with the large live trout. They stayed on the safe side of the screen—and survived.

River Test. Kanayama plans to hold his next test in the Chitose River on Hokkaido Island. He will release educated baby trout, marked so that they can be recognized, in a stretch of water stocked with hungry and cannibalistic grown-up fish. Marked, unschooled babies will be released also. After a suitable interval, the young trout will be netted to see whether the educated ones have survived better than their unshocked cousins.

Kanayama is sure that his pupils will pass the test, and he hopes to build a mass-education plant: a channel with a long series of electrified tin fish. Small trout passing through it will get scare after scare and emerge fully trained for life in a dangerous river. But the biologist is still bothered. Why should successful students grow to bright-colored maturity only to be caught on an angler's hook? "I have become so fond of the lovely rainbow trout," he says with a tender smile, "that I may start another project to teach them to stay away from hooks. It should be easy enough. Rainbow trout are really smart."