Why So Blue, Fish and Frogs?

Dan Snyder was mowing his lawn in North Hudson last month when he noticed a blue bullfrog beneath a rose bush. Also this summer, anglers on Rock River, which flows into northern Lake Champlain’s Missisquoi Bay, caught a yellow perch and a sunfish that had a turquoise tint. And Lake Colby, in Saranac Lake, has long produced a silvery-blue variant of “yellow perch.”

These three shades of blue may represent three different phenomena, only two of them explainable. Let’s start with the blue perch of Lake Colby.

Blue perch from Lake Colby, in Saranac Lake. Photo by Rich Preall, NYSDEC

Blue perch are rare but not that rare. They are genetically abnormal in that they lack yellow pigment, so the typical perch colors of yellow, green and orange do not appear. At least one in every 50 fish caught in Lake Colby is blue, a relatively high concentration, according to Department of Environmental Conservation (DEC) surveys. The variation seems to cluster in certain lakes, where the blue fish can interbreed. Northern pike and walleye are also known to have localized concentrations of blueish fish, though not in the Adirondacks.

I have a blue walleye in the freezer, caught near Temagami, in north Ontario, where they are pretty common. This fish is a little different, though. Like the Lake Colby perch, it lacks yellow pigment. But it was also covered by a blue-jay-blue mucus, which you can see when it rubs on snow or white clothing, or if you scrape it off. If you click to enlarge the photograph of yellow perch from Canada [below] you can see that the blue fish is bluer than the Lake Colby perch, and the mucus also covers the yellow fish—most visibly on its cheek.

Canada-caught yellow perch with blue mucus (blue and yellow morphs). Photo by Wayne Schaefer

Wayne Schaefer, a professor at the University of Wisconsin, caught these fish. He has studied the phenomenon of blue walleye in Quebec and Ontario for years. His theory is that an excess buildup of biliverdin in the blood is excreted through the skin and is picked up by a protein carrier molecule he identified and labeled sandercyanin, Sander for the genus name of walleye and cyanin for the color.

The scarcity of sandercyanin south of the U.S.–Canada border, its peak in August, and its presence on only the topside of the fish leads Schaefer and fellow researchers to hypothesize that the phenomenon is linked to solar radiation. Sandercyanin might be acting as sunscreen. Cancer-causing UV rays are stronger closer to the North and South Pole, where ozone is depleted.

So, back to the Adirondacks: Looking for an explanation for his blue bullfrog, Dan Snyder found Wayne Schaefer via his website, The frog could be another genetic variant. But if it’s not an isolated case, Schaefer says blue might be a manifestation of sunscreen in amphibians also. “The color is on the dorsal side of the frog, that’s an indication it could be related to solar input rather than pollution,” he says.

Whatever is tinting the fish in Rock River, near the Quebec border in Vermont, is another story altogether. If you begin watching at the 7:28 point of this report by PBS’s Mountain Lake Journal, you will see that the blue on the Rock River perch and sunfish appears to be concentrated around the mouth. It can also be seen on the underside of the mouth. (There also appears to be yellow pigment in both the perch and sunny.) Mississquoi Bay is surrounded by industrial agriculture and suffers frequent toxic blue-green algae blooms, and there was a bloom in progress when the fish were caught.

Schaefer cautioned against linking fish coloration to algae—it’s never been done. And Vermont DEC officials say the fish samples were too deteriorated to provide any conclusive information. “We still don’t have a clear idea of what caused the discoloration in the two fish from the Rock River,” Rich Langdon, chief of Biomonitoring and Aquatic Studies, emailed. “The thinking is that is probably not the rare melanin abnormality that occurs in fish (and sometimes in frogs—my neighbor has a blue green frog in his pond). An examination of the perch revealed nothing out of the ordinary.” If anyone catches another blue-tinted fish in Rock River or Mississquoi Bay, Vermont Fish & Wildlife officials would be interested in seeing it while it’s still fresh.

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