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Tohru Murakami via Flickr Creative Commons // CC BY-NC 2.0

A Fish Parasite May Have Compromised Decades of Behavioral Experiments

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Tohru Murakami via Flickr Creative Commons // CC BY-NC 2.0

Science’s image as an objective collection of facts took another hit this week, as researchers report that a common fish parasite may have skewed the results of thousands of behavioral science studies. They published their findings in the journal Fish Diseases.

Pseudoloma neurophilia is a teeny-tiny type of parasitic fungus called a microsporidium. Microsporidia are prolific and diverse, infecting almost every type of animal on Earth. Symptoms of a microsporidium infection vary by parasite and host species. Sometimes it’s fatal. Other times the effects are so subtle that you’d really have to be looking to notice them.

Fortunately, some scientists are looking. Researchers in the biomedicine and microbiology departments at Oregon State University (OSU) have been tracking P. neurophilia for years—specifically, its effect on Danio rerio, commonly known as the zebrafish.

If you follow science news, you’ve probably heard about zebrafish before. These unassuming little fish have become some of the most popular research animals in the world, thanks to their low-maintenance lifestyle, susceptibility to drugs and genetic changes, and enormous broods. They’re also incredibly social, which has led researchers to consider them a good model for people. Consequently, we use them to test pharmaceuticals, hunt for clues to genetic disease, and even explore the roots of human behavior.

Studies of D. rerio’s social activity often center around one specific behavior: huddling. Stressed zebrafish band together in groups called shoals, while healthy, calm fish tend to spread themselves wider apart. So researchers generally assume that clustering fish have been negatively affected in some way by experimental treatment, whether that’s a drug or a gene associated with disease.

But there’s more to it, say the OSU scientists. Their studies of P. neurophilia suggested to them that the parasite could be quietly changing zebrafish behavior. To find out, they brought 140 zebrafish into the lab and divided them into 12 tanks of 10 fish and one “sentinel tank” of 20. They set up cameras by the 12 test tanks and took still images at regular intervals.

Then, the team added water to all the tanks. Six exposure tanks, and the sentinel tank, were topped up with water from a tank of infected fish. The remaining six tanks got water from a parasite-free tank.

Once again, the researchers trained their cameras on the swimming fish, monitoring their movement. Analysis of the tank snapshots showed that fish exposed to the parasite were more likely to stick together than fish in the clean tanks. The researchers noted that fish in the parasite-treated tanks stuck even more closely together than fish in other studies who had been dosed with stress-inducing chemicals.

Postmortem examinations of fish from each group confirmed that the presence of P. neurophilia in the water was more than enough to infect a tank’s inhabitants. None of the fish from the control tanks were infected, but nearly all the fish from the parasite-treated tanks were.

The team’s earlier work has shown that infection with the microsporidium is very, very common in laboratory zebrafish populations. Lead author and veterinary surgeon Sean Spagnoli noted that some researchers might not even check to see if their fish are sick.

“I haven't seen a single paper that stated that ‘fish used were certified pathogen-free for P. neurophilia'," he told Nature.

This wouldn't be the first time scientists have overlooked a big variable. A study published earlier this year found that lab mice get chilled, stressed, and sick at normal laboratory temperatures. Another concluded that software design issues may have led to false positives in thousands of brain scan studies.

University College London geneticist Elena Dreosti isn't sure that's what's happening here. Speaking to Nature, she argued that the study’s results are statistically weak.

“Considerable additional work is needed to know if this is likely to have a significant impact on the type of behaviour research that is done by the community working with zebrafish,” she said in Nature. Other researchers have expressed doubts about the precision of measuring intra-fish distances through snapshots.

The OSU team stands by their methods and findings, but will continue to study the issue.

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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.

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