A Blue Mystery
By: Gord Ellis
Scientists continue to scratch their heads over the makeup of northwestern Ontario's blue walleye
Many years ago, I spent a summer working for the Ministry of Natural Resources, along with a handful of other high school students, obtaining small random samples of various fish for inventory assessment. It was fascinating, but gruelling work. You haven't really lived until you've popped long-dead, reeking suckers out of a gill net in 30°C heat.
That summer, while lifting nets in a lake up the Boreal Road, north of Thunder Bay, I saw my first blue walleye. The fish was mixed in with a bunch of normal-looking yellow walleye, but it stood out, largely because it was the colour of a not-quite-ripe blueberry. Since that summer nearly three decades ago, I've caught a couple more blue walleye in other places across northwestern Ontario, including the Albany River.
The blue walleye is a genuine oddity. It's found in scattered spots throughout northwestern Ontario, including Thunder Bay, Ear Falls, Red Lake, and the Pickle Lake area. There are also reports of blue walleye in other areas of Ontario, Quebec, Manitoba, and, increasingly, in the northern United States.
We know this because the blue walleye is the focus of an in-depth study led by Dr. Wayne Schaefer of the University of Wisconsin, Washington County. He says his interest in the fish was a result of actually catching some of them in northwestern Ontario.
"I've owned a cabin in the Ear Falls area for about a decade," Schaefer said. "I've done a lot of fishing in the area and have encountered blue walleye there. I began asking at sport shows if any outfitters had blue walleye in their lakes and if I could go in and take a closer look at them. I found several, and have been tracking blue walleye from the Lake Nipigon area all the way up to the Cobham River in northeastern Manitoba." So why all the excitement about what seems to be just an odd colour phase of the garden-variety walleye?
"They're different," said Schaefer. "You don't see them every day. They're often found in isolated conditions in the upper end of river systems.
The other reason for interest in blue walleye is a little more serious, says Schaefer. There was once another blue walleye known as the "blue pike." It was a key commercial fish in Lake Erie. Sadly, the fish has been extinct for decades, but news of blue walleye in northwestern Ontario turned the heads of fisheries managers throughout the Great Lakes region. There have long been rumours these blue walleye might be the ancestors of stocked blue pike, although there's little evidence this is the case. Dr. Schaefer says during the blue walleye study they had hoped to find a connection between the two fish. The genetics proved otherwise.
Not the Same
"The fish we're getting from Ontario are different from preserved museum specimens of Lake Erie blue pike," he said. "But they share some characteristics. The blue walleye and blue pike appear to have larger eyes and they're closer together then normal yellow walleye. They're blue. We wonder if the mechanism of colouration for blue walleye was the same as what was found in the blue pike of Lake Erie."
Initially, Schaefer says he considered two different theories that might explain the blue colouration. One theory was the fish lacked yellow pigment, which could have been caused by a single gene mutation. In other words, the blue fish were simply not producing the normal yellow colour. The second theory was the possibility of a blue pigment in the mucous of the fish. Schaefer noted in some lakes that have blue walleye, a slight blue pigment was also found in yellow walleye. He believed the cause of this was probably one of two things: a secretion from the mucous glands of the fish and/or a symbiotic micro-organism living in its mucous. Last year, he finally got his answer.
Working in collaboration with a biochemist from the University of Iowa, the chemical constituent of the blue pigment was found in the mucous of the fish and identified. It's a protein never before described in literature. The researchers have named the pigment "Sandercyanin." Sander is the genus name for walleye and cyanin means blue in Greek.
"Sandercyanin consists of a protein that carries biliverdin, a bio-product that comes from the breakdown of heme (a protein) in blood," said Schaefer. "It's being excreted into the mucous in the skin of walleye and is being picked up by a large protein-carrier molecule, where it takes on this beautiful blue colour typical of blue walleye." Schaefer says Sandercyanin doesn't harm the health or taste of the fish.
With the mucous/colour connection confirmed, the researcher began looking at why this was happening. Schaefer says biliverdin (pronounced billy verdun) is a toxic material that has to be excreted from the body, usually in urine. Blue walleye, however, are secreting it through their skin. Schaefer says he can only speculate about what's causing the breakdown of heme into biliverdin at high levels, but he has a theory.
"We know the literature contains information that ultraviolet radiation from the sun does cause the breakdown of heme into biliverdin," he said. "More blue colour is produced in late summer than in winter or spring. The literature also suggests that biliverdin might act as a sunscreen in some species of animals. If this was the case, it would certainly be a remarkable feat of nature."
Schaefer is quick to point out the theory is speculative - an hypothesis. He notes, however, it's supported by literature. He says if increased ultraviolet radiation, due to depletion of ozone from human pollution, causes production of a compound in walleye blood that acts as a sunscreen, it would be an example of nature protecting itself using the very product that's being formed from the pollution.
While some of the mystery around blue walleye has been removed, there are still more questions than answers. This past March, Dr. Schaefer joined some of his students in northwestern Ontario, catching and sampling blue walleye. They also plan to return this spring. They hope to quantify the seasonal production of blue pigment and will also be looking at the skin histology of these fish to see what cells are producing the blue pigment.
For more information on the study or to report a blue walleye, go to www.bluewalleye.com.