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Timothy Knepp, U.S. Fish and Wildlife Service via Wikimedia Commons // Public Domain

Scientists Say Light Colors Make Salmon More Belligerent

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Timothy Knepp, U.S. Fish and Wildlife Service via Wikimedia Commons // Public Domain

Marketers have long known the power of color to manipulate consumers. Red and yellow supposedly make us hungry, while blue can calm us down. Apparently, we’re not alone in our subconscious response to color; scientists say salmon kept in tanks with black backgrounds were four times less aggressive than those in light blue tanks. The findings were published last week in the journal PLOS ONE.

Fish consumption is on the rise, and a lot of that demand is met by a growing aquaculture (fish farming) industry. But even as consumers begin to demand beef and eggs from humanely raised cows and chickens, few have given fish welfare much thought.

Fortunately, scientists have. A large body of research indicates that fish are incredibly visual animals and are very sensitive to the appearance of their environments. Previous studies have shown that even the colors of gravel and light filtering through the water can affect fish health, fertility, and aggression. But nobody had considered the potential influence of background color until researchers from the University of British Columbia’s Animal Welfare Program decided to take a look.

The scientists brought in 100 Coho salmon (Oncorhynchus kisutch) and divided them into 10 tanks of 10 fish. Every day, each tank was lined with a piece of laminated paper divided into two different colors: either black with white, light gray, dark gray, or a pattern; and light blue with white, light gray, dark gray, or black. This way, the fish could swim to the side of the tank backed with the color they liked better. Each tank was equipped with a camera that filmed the salmon from above. Afterward, the researchers watched each tape and recorded how the fish behaved, as well as how many fish chose each color.

The salmon had very clear preferences. Time and time again, they opted to stay in front of the darkest background available. When they could have black, they chose black; in the absence of black, they settled for dark gray. And even when they weren’t on the darker side of the tank, just having a black or gray section in the tank seemed to soothe the fish.

The reverse was also true. Like Morticia Addams, the salmon seemed almost offended by pastels. When the fish were forced to endure light blue backgrounds they became four times more aggressive than they were in black-backed tanks, chasing, charging, and even biting their tank-mates.

Why does this matter? Well, guess what color is currently the default for salmon fishery tank backgrounds. Did you guess light blue? You’re right.

The researchers note that their study had some limitations. The fish they studied were all the same age, and a salmon’s aggressive tendencies do vary over its lifespan. They also didn’t test the effects of water temperature and season. Still, this is progress towards a better understanding.

“Fish both preferred and were dramatically less aggressive in darker backgrounds,” co-author Marina Keyserlink said in a press statement. “Thus, we found a relatively simple environmental modification that has the potential to improve animal welfare."

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Animals
Watch a School of Humpback Whales 'Fish' Using Nets Made of Bubbles 

Just like humans, humpback whales catch many fish at once by using nets—but instead of being woven from fibers, their nets are made of bubbles.

Unique to humpbacks, the behavior known as bubble-net feeding was recently captured in a dramatic drone video that was created by GoPro and spotted by Smithsonian. The footage features a school of whales swimming off Maskelyne Island in British Columbia, Canada, in pursuit of food. The whales dive down, and a large circle of bubbles forms on the water's surface. Then, the marine mammals burst into the air, like circus animals jumping through a ring, and appear to swallow their meal.

The video offers a phenomenal aerial view of the feeding whales, but it only captures part of the underwater ritual. It begins with the group's leader, who locates schools of fish and krill and homes in on them. Then, it spirals to the water's surface while expelling air from its blowhole. This action creates the bubble ring, which works like a net to contain the prey.

Another whale emits a loud "trumpeting feeding call," which may stun and frighten the fish into forming tighter schools. Then, the rest of the whales herd the fish upwards and burst forth from the water, their mouths open wide to receive the fruits of their labor.

Watch the intricate—and beautiful—feeding process below:

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Big Questions
Why Do Dogs Love to Dig?
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Dog owners with green thumbs beware: It's likely just a matter of time before Fido turns your azalea bed into a graveyard of forgotten chew toys. When dogs aren't digging up your prized garden, they can be found digging elsewhere in your yard, at the beach, and even between your couch cushions at home. But what exactly is behind your dog's drive to turn every soft surface he or she sees into an excavation site?

According to Dr. Emma Grigg, an animal behaviorist and co-author of The Science Behind a Happy Dog, this behavior is completely normal. "When people say 'why do dogs dig,' the first thing that always comes to mind is 'well, because they're dogs,'" she tells Mental Floss. The instinct first appeared in dogs' wolf ancestors, then it was amplified in certain breeds through artificial selection. That's why dogs that were bred to hunt rodents, like beagles and terriers, are especially compelled to dig in places where such animals might make their homes.

But this tendency isn't limited to just a few specific breeds. No matter their original roles, dogs of all breeds have been known to kick up some dirt on occasion. Beyond predatory urges, Dr. Grigg says there are two main reasons a dog may want to dig. The first is to cool off on a hot day. When stuck on an open lawn with little to no shade, unearthing a fresh layer of dirt untouched by the sun is a quick way to beat the heat.

The second reason is to stash away goodies. Imagine your dog gets bored with chewing his favorite bone but knows he wants to come back for it later. Instead of leaving it out in the open where anyone can snatch it up, he decides to bury it in a secret place where only he'll be able to find it. Whether or not he'll actually go back for it is a different story. "There's a disconnect with modern dogs: They know the burying part but they don't always know to dig it up," Dr. Grigg says.

Because digging is part of a dog's DNA, punishing your pet for doing so isn't super effective. But that doesn't mean you should stand idly by as your yard gets turned inside-out. When faced with this behavior in your own dog, one option is to redirect it. This can mean allowing him to dig in a designated corner of the yard while keeping other parts off-limits, or setting up a raised flowerbed or sandbox especially to satisfy that urge. "You can get him interested in the area by burying a couple bones or some interesting things in there for him to dig," Dr. Grigg says. "I like the idea of buried treasure."

If your dog's motive for digging is more destructive than practical, he may have an energy problem. Dogs require a certain amount of stimulation each day, and when their humans don't provide it for them they find their own ways to occupy themselves. Sometimes it's by chewing up shoes, toppling trash cans, or digging ditches the perfect size for twisting ankles. Fortunately, this is nothing more walks and playtime can't improve.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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