Brook trout ID’d by their ‘fin prints’ Unity College senior makes discovery

UNITY – A school of swirling, polka-dotted, red-bellied brook trout rushes to the surface when a visitor leans over their tank in the wet laboratory of Unity College. Once food is tossed in, the water boils with the fish fighting for the treats, breaking the surface and slapping the water with their tails upon re-entry.

To the untrained eye, they all look the same.

Jason Overlock, a senior research student at the college, claims, however, to have made a new scientific discovery that allows researchers or anglers to tell one trout from another.

“I’m getting kind of excited about this,” Overlock admitted Friday, adding that the discovery could have future applications in medical and environmental research.

Confirming what some fishing experts have guessed at, Overlock, 30, of Winslow, has determined that brook trout have individualized dorsal fins, “fin prints” as he calls them, that allow observers to tell one fish from another.

“Whales can be identified using the markings on the fluke,” A. Jim Chacko, Unity College professor of aquaculture, said Friday. “It has been said that elephants can be identified by the markings on their ears. Now the individuals within a brook trout species can be identified using the markings on their dorsal fin.”

Chacko said he has been unable to find similar research or conclusions in any published studies of brook trout.

The professor said the immediate implication is that testing and research done on brook trout no longer will have to be invasive, such as cutting or clipping a fin for identification.

“Using our system, you can identify Tom, Dick and Harry among the brook trout. Maybe even Henry and Martha,” he said.

Future applications could involve medical testing done on fish and allow researchers to identify specific fish in a study by their fins. “There may be more, even wider applications,” Chacko said.

Working in Unity College’s wet laboratory, which is a series of rooms filled with tanks and fish, Overlock suddenly noticed in late winter that he could tell the fish apart by the patterns in their dorsal fins. He also could tell which were farm-raised and stocked and which had been raised in the wild.

“The fins are not so wormy and mazey,” Overlock explained. He was not referring to parasites, but rather to the unique swirling patterns on the fish’s dorsal fins.

The fish being reared in Chacko’s lab are beautiful. The brook trout’s general body color is dark green. Looking closer, its back is dark olive-green or gray-green, mottled with dark, squiggly or wormlike markings from head to tail. The sides have scattered red dots, surrounded by bright blue halos. The belly is usually pale yellow-orange, with a blackish or gray streak down the middle.

Overstock had set up six fish in a natural-habitat tank and while working with them and feeding them daily, noticed the difference in the fins. “I doubted what I was seeing at first,” he admitted. “I just kept checking and checking.”

Overstock brought his findings to Chacko, and the pair developed a technique to individually photograph the fish and then transfer the patterns on the dorsal fin into black and white images.

“The results were astounding,” said Chacko. “No two dorsal fins looked the same. I slapped my forehead with my hand and said, ‘We were missing the most obvious!'”

The pair expanded the project to include 60 fish, and Overstock began an independent study. By this week, they were ready to release their findings and begin a search for funding to expand the project.

“The next step, which will take $10,000 to $15,000, will be to keep 20 of the original fish in the system and monitor them to see if this changes over the long term,” Chacko said. He said he would like to develop a computer program, similar to the FBI’s fingerprint program.

Mark Tardiff, an associate director at the college, said the study could be linked with other aquaculture and environmental programs at the school. “For example, fisheries students are currently doing technical trials in Unity Pond,” Tardiff said. “There could be a combined research project involving both disciplines.”

When brook trout are kept in captivity, they often go blind, Tardiff said. “By being able to identify individual fish, studies can be conducted in the wild and prevent things like the blindness happening in captured fish,” he said.

Unity College, an environmental college, graduates the greatest number of environmental students each year in the entire country, Tardiff said. “That’s 100 to 120 a year. Our graduates are currently owning and working in fish farms, fisheries, academia, and research facilities all over the country. Students like Jason here are sought after.”

The school will be seeking future funding to continue Overlock’s work. Despite his graduation on May 14, Overlock hopes to remain involved in the project.

He already has had several environmental job offers, he said, but if he remains in Maine, he will use his spare time to continue work on the identification project.

BANGOR DAILY NEWS PHOTO BY LINDA COAN O’KRESIK

Jason Overlock, a senior research student at Unity College, has discovered that brook trout can be identified by the markings on their dorsal fin.