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article imageMystery of the neon-green jackfish has been solved

By Karen Graham     Aug 28, 2015 in Science
A fluorescent green northern pike caught earlier this week in Canada's Great Slave Lake created quite a stir on the Internet as readers put forth various opinions on why the unusual fish got its coloration.
Randy Straker and his fishing buddy Craig Thomas, are avid fishermen, and have been working their way around the lake for the past five years, testing new sites, looking for the perfect spot, says CBC News.
A northern pike  Esox lucius  with normal coloration.
A northern pike, Esox lucius, with normal coloration.
Jik Jik
They were finishing up their day, fishing in a new area, the North arm of Great Slave Lake on Sunday, when Randy had a hit on his line. After reeling the fish up along side the boat, the friends saw it was a northern pike, or jackfish, and it was a bright, fluorescent green.
But Randy, who happened to be wearing polarized sunglasses, had to look twice. The fish looked odd for some reason, and when he removed his glasses, thinking the lens were creating the unusual color, he realized, as did his friend Craig, that they had a very strange fish indeed.
The pike had a bright green body and when they brought it up beside the boat, it flared its gills and they could see right down its throat, and the throat was a bright blue. Craig started snapping pictures when Randy pulled the fish into the boat. The men estimate the fish weighed between 12 to 14 pounds and was about 38 to 40 inches long.
The pike s unique coloring stands out next to a photo of a more traditionally colored jackfish.
The pike's unique coloring stands out next to a photo of a more traditionally colored jackfish.
Craig Thomas/Social media
Randy told the CBC, "In hindsight, after looking at the pictures, we should have taken a whole lot more. But we compared some pictures that we'd taken previously of a fish. And when you put it up against another pike, it's way lighter. The fins were kind of a translucent green as opposed to the darker colors of a regular pike."
Both men say they have never seen anything like the strange colored fish. Straker says he has seen some fish with partial albino coloration, and even a few fish that have spots on their bodies where coloration is absent, but never a green fish. He posted pictures to his social media account and the theories started coming in.
"We thought maybe diet... maybe whatever it got into eating, but nothing concrete. The biologists that have given any feedback have suggested that they have no clue really what's caused it," Straker said. But biologists will never get to examine the pike. The guys let the unusual fish go beck into the lake to live another day.
The mystery may have been solved
The mystery of the fluorescent green pike may have been solved. According to CBC News, Jeff Goudreau is a fish and wildlife technician and a fishing guide who has worked on Great Slave Lake for many years. He says he recognized the coloration right away when he saw the pictures.
"I've probably caught three or four of those in my life," he said. "And I know a lot of other guides in Canada in other lakes that have caught similar ones." Goudreau attributes the strange coloration to something called "chromatophores."
A good example of the use of chromatophores is seen in the Blue-ringed octopus. This one was found i...
A good example of the use of chromatophores is seen in the Blue-ringed octopus. This one was found in New South Wales, Australia.
David Breneman at English Wikipedia
"Most people understand chromatophores from seeing cephalopods in the ocean, like squid or whatnot," explained Goudreau. "They change color when they're scared, or they're getting ready to attack something. Pike do the same kind of thing, but on a lower level."
Goudreau goes to explain that pike hunt near the surface of the lake, where the water is a lighter blue and the sun is brighter. Being predatory, the pike also spend their time near and around reeds, which are often full of green algae growth.
"They try to blend themselves into that environment to be better hunters," he said. "So you'll see those aquamarine colors, where the throats are very blue and dark green and stuff. That's pretty much what's happened, with that one."
Neville Fickling is a zoologist from England who's written a number of books on pike, agrees with Goudreau's explanation. He says the fish are "always going to determine exactly what their environment is, and adapt the chromatophores accordingly." Fickling adds that all fish are able to adjust their chromatophores, and some fish can change their colors more quickly and with greater intensity.
Great Slave Lake is North America's deepest lake
The coloration of northern pike in Great Slave Lake can vary, depending on where the pike's hunting grounds are located. Goudreau says he has caught dark brown pike in areas where lots of logs are in the water. He says that because of the lake's size and depth, a person can see many variations in coloration of the pike.
Great Slave Lake  Northern Bay  NWT  Canada.
Great Slave Lake, Northern Bay, NWT, Canada.
David Adamec
Great Slave Lake is the second largest lake in Canada's Northwest Territories after Great Bear Lake, but it is the deepest lake in North America at 614 meters (2,014 ft). Adding to these impressive statistics, the lake is the tenth largest lake in the world.
Given the fact that Great Slave Lake is so deep, it is ideal for the northern pike. This fish prefers waters that are below 25 degrees Celsius. Rising air temperatures could impact the pike's distribution in many shallower lakes and slow-moving rivers, though. Warming temperatures would also effect the pike's ecosystem, impacting the availability of food.
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