UM professor attempts to take rockfish to school

February 07, 1993|By Douglas Birch | Douglas Birch,Staff Writer

COLLEGE PARK -- School's open, and Dr. Arthur N. Popper's 19 wide-eyed students are in over their heads.

That isn't surprising, considering his pupils are young striped bass, or rockfish. Dr. Popper, chairman of the University of Maryland's zoology department, is trying to do what no one has done before: train rockfish to come when they're called.

Working with a $30,000 grant from the Maryland Institute for Agriculture and Natural Resources, Dr. Popper hopes to make life easier for Maryland fish farmers. In aquaculture ponds, they raise 440,000 pounds annually of the succulent fish -- worth almost $1.1 million.

By beckoning rock to their meals, he said, farmers can cut the amount of feed lost when it drifts uneateninto the muck below. It would also be easier to count and to administer medicine to fish who feed on command.

Perhaps, he said, farmers will one day be able to train adults and juveniles to respond to different sounds. That way two generations could be kept in the same pond, and the adults easily separated for feeding, census-taking and harvest.

Training fish to respond to one sound and ignore another will be tricky, he said.

"It's a far-fetched hypotheses, but one well worth testing," he said.

The training apparatus is simple. The farm-raised rockfish, all about 6 months old, swim in a tub about 4 feet across. Above the tub is a frame built by graduate assistant Rebecca Hedreen. It is intended to hold a video camera, an automatic feeding machine and a speaker.

During a recent tour of the lab, the speaker wasn't in place yet. And, so far, the scientists have had a hard time finding a food that suits the fish.

But once everything is set up, a computer will be programmed to activate the equipment. Every 20 or 30 minutes, a 10-second, low-pitched tone will blare and the feeder will spit out about a dozen pellets.

Eventually, Dr. Popper said, he hopes the fish will swarm beneath the feeder every time they hear the hum -- the way Russian physiologist Ivan Pavlov trained dogs to salivate every time they heard a certain sound.

One key question is whether rockfish can hear.

Dr. Popper thinks so, though no one has proved it.

"Based on what I know about fish hearing, which is basically as much as anyone in the universe knows, these guys can hear," he said.

But they may not hear very well. Dr. Popper thinks rockfish probably can hear sounds up to 400 or 500 cycles per second. (The frequency and pitch of a sound are measured in cycles per second. The more cycles, the higher the frequency and the pitch.)

Goldfish can hear sounds up to about 3,000 cycles per second. Humans can hear sounds that range from less than 50 cycles to more than 20,000 cycles per second.

Roy A. Castle, aquaculture project manager with the state Department of Agriculture, said a method for training rockfish to respond to sound signals would be particularly useful to farmers who use automatic feeders.

Those who feed their fish manually find the fish generally learn to spot them coming -- though some fish linger at the fringes of the pond and don't realize what's happening until "the feeding frenzy starts," Mr. Castle said.

Automatic feeders can take the fish by surprise.

"In a pond system, it might cost you $1.75 to raise a rockfish to market," he said. "But it might cost you $1.50 by raising the efficiency of feeding, where every pound of food is used to its maximum."

Dr. Popper has worked with Dr. Paul Patrick of Ontario Hydro in Canada, who has had some success teaching walleye, bass and sturgeon to swim toward a given sound.

Other scientists have taught oscars, goldfish and squirrel fish from Hawaii to perform relatively complicated tasks, such as pushing a series of paddles on command.

Japanese and Russian fishermen have tried teaching various commercial fish to come when they ring a bell or sound a horn, and then released the trained fish into bays or large lakes. While these trainers have claimed success at getting the fish to gather at meal and harvest times, Dr. Popper suspects that the fish might simply hang around the spot where they know they will be fed, or return there periodically to see if luncheon is served.

Dr. Popper is not trying to develop a machine that would call wild rockfish, though he says he's received inquiries from fishermen about this.

Dr. Popper says there are no plans to release trained fish in the bay and that his signal only would attract graduates of his course.

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