After six years of studying freshwater fish, Grant Brown thinks he may be on the brink of making an impact on the fishing community and the millions of people who participate in one of the most popular sports in the world.
Brown, an assistant professor of biology, has been conducting research on Ostariophysans, the largest group of freshwater fish. He has focused on the evolution of chemical communication in fish, especially minnows and trout, and thinks that if fish can be conditioned to recognize predators, the chances for survival may improve dramatically.
Brown's research combines his lifelong interest with research that goes back sixty years.
A fisherman since he was a youngster in Nanaimo, British Columbia, Brown began studying neuroanatomy in fish as an undergraduate at the University of Lethbridge in Alberta. He worked with salmon and trout as a graduate student at Memorial University in Newfoundland, then switched to minnows and small bait fish during his postdoctoral fellowship at the University of Saskatchewan.
The sixty-year-old research was done by a scientist named Karl von Frisch, who discovered that European minnows had a chemical in their skin that, when released into the water, warns other minnows of a predator environment. Little had been done with that research until Brown and his colleagues at the University of Saskatchewan and Mount Allison University in Canada began to study the alarm pheromones — chemicals produced and stored in cells in the minnows' skin. Released into the water when the skin is damaged by a predator, the chemical is immediately detected by other minnows, warning them of danger.
“When they detect it, they show stereotypical anti-predator responses,” Brown explains. “They dash down to the bottom, seek cover, and avoid those areas for periods of at least six to eight hours. They obviously do this to increase their probability of surviving.”
The predators also respond to the alarm pheromone, using it as a foraging tool, or actually to “smell” their food. For example, since a pike can detect minnow alarm pheromone, it will seek areas where it senses this pheromone, which indicates that minnows are nearby.
The ability of fish to communicate chemically may be the key to improvements in habitat and fisheries management, Brown explains. In many places, heavy fishing pressure and environmental problems have threatened fish populations. As a result, the Fish and Wildlife Service regularly raises fish and restocks threatened waterways. In New York State alone, for example, the Department of Environmental Conservation releases more than one million pounds of fish into 1,200 public streams, rivers, lakes, and ponds.
The problem is that very few of these fish survive in the wild. “Upwards of seventy to eighty percent of hatchery juveniles die within the first three weeks that they are released into natural waterways because they don't recognize predators,” he says.
But perhaps the hatchery fish, which include trout, salmon, and char, could be conditioned by using the alarm pheromone system to train them to recognize predators. To examine this possibility, Brown is conducting research in several different areas, often simultaneously.
In one project, he has been using the alarm pheromone in conjunction with a visual or chemical cue of a predator to condition trout to recognize and respond with the appropriate anti-predator behavior.
“If you show a minnow the visual cue of a pike or the odor of a pike, it won't respond,” he says. “Minnows will only respond once the visual or chemical cues of the predator have been paired with an alarm pheromone. We have found that a single exposure of the alarm pheromone in conjunction with a visual cue or chemical cue of a pike (pike odor, for example) is enough to condition the minnow that that cue indicates danger.”
The approach works much like Pavlov's dog — the fish learn to associate the alarm pheromone response (seeking cover) with a visual or chemical cue of their predator, though the two are not really related. When minnows are exposed to the alarm pheromone, they immediately respond with anti-predator behavior. Yet, when they are exposed to a visual or chemical cue of pike prior to their conditioning, they do not respond at all.
Working in his lab, Brown and his student researchers have developed a system to “trick” minnows into associating the alarm pheromone response (seeking cover) with the visual or chemical cue of the predator. They release the alarm pheromone into the water just as the minnow senses the cue from a pike — usually a skin extract — and the minnow naturally responds to the pheromone with anti-predator behavior. But the minnow also learns to associate that response with the cue from the pike. Soon, the minnow responds as if an alarm pheromone were released when it senses a pike — even though there is no pheromone present. Thus, it learns to better protect itself from danger.
Since rainbow trout and coho salmon have skin alarm systems similar to those in minnows, Brown speculated that they could also be conditioned to exhibit anti-predatory behavior. He found this to be true.
“We can take that alarm pheromone, present it to a fish in a hatchery along with the odor of their major predators, and condition them in a hatchery setting before releasing them into the wild,” he says. “We found that they can retain their recognition of predator odor for at least twenty-one days, the critical period for their survival.”
Brown is also working with Jim Adrian, assistant professor of chemistry, to try to determine the exact chemical structure of the alarm pheromone in minnows. “This is a biochemical approach to trying to isolate the chemical cue and manipulate and synthesize chemicals to figure out exactly what the fish are responding to,” he explains.
A series of experiments has revealed that nitrogen oxide is likely the single functional group that elicits the response in fish. To prove this, they injected various chemical compounds into tanks and tracked fish behavior before and after injecting the control or the experimental stimulus. They verified their lab results in the field by setting minnow traps in local waterways and attaching a piece of cellulose sponge saturated with either distilled water or one of the experimental cues wired to the trap.
“If the chemical was acting as an alarm pheromone, then we would get very few fish in the trap, which is what we found for the nitrous oxides,” he says. “This is potentially very useful because if we can figure out what chemical the minnows are responding to, maybe the trout are going to respond to that same chemical, and now we have a cheap, economical, synthetic pheromone to condition the trout or salmon.”
If this proves to be true, conditioning fish in hatcheries could quickly become a reality. Chemists could mass produce the synthetic alarm pheromone that fisheries management teams could use to condition the millions of juvenile fish they rear each year.
Brown is now looking at further implications of the alarm pheromone, especially how it is affected by acid rain situations. Early studies have indicated that minnows in low pH situations (a result of acid rain) do not respond at all to the alarm pheromone, but those same minnows respond appropriately when the pH is raised to a normal level. This could be one reason acid rain is having such a detrimental effect on our ecosystems.
“Minnows and dace and darters and all of the fish that have this signal seem to be unable to respond to the presence of that signal in acid rain situations,” Brown says. When these fish do not respond to this chemical cue, the likelihood that they will die increases dramatically — something that affects the entire food chain. “It could have a considerable ecological impact,” he says.
Brown is conducting further study in the field, collecting fish from acidified lakes in the Adirondacks and testing their responses to the alarm pheromone. When his studies are complete, they could provide a valuable clue as to how fish are harmed by acid rain and how “dead” lakes evolve.
Brown plans to continue his research in pinpointing the molecular structure of the alarm pheromone and to expand his studies into how other species of fish respond to the alarm pheromones. His findings have begun to attract attention in the fishing community, and the Washington State Fish and Wildlife Department plans to test his conditioning system for coho salmon in hatcheries. Improving the chances for juveniles could substantially increase the number of sport salmon catches in the state, now about a half million a year.
But the impact will go far beyond recreational fishermen. If Brown's conditioning system proves successful, we all could be eating more fish — and many of those fishing stories we hear could turn out to be a lot closer to the truth.