You asked. Ars answers. Here’s how to run an MRI on an electric eel


Enlarge / Chicago’s Shedd Aquarium vets have come up with many unusual procedures to diagnose and treat the animals they care for, including trying to run MRI scans on electric eels.

Right before Thanksgiving, we shared how the Shedd Aquarium in Chicago resolved the curious case of the missing chloroquine. The pest control drug is usually added to the water for new quarantined animals, but it mysteriously went away. The culprit: hungry and hungry germs. The post included a throwaway line on how aquarium vets also had information on how to give an electric eel an MRI.

This track seemed to resonate with readers, and we received several questions about how, exactly, this feat could be accomplished. You asked. We wanted answers. So we turned to Bill Van Bonn, the clinical veterinarian in charge of the Aquarium’s Animal Health and Welfare Center, who has a state-of-the-art veterinary hospital to monitor the health of the aquarium. all animals in the shows and treat them as necessary. Dr Van Bonn and his colleague Dr Karisa Tang were happy to help.

Van Bonn describes the aquarium veterinary team as “family physicians” rather than specialists, although they can draw on world-class expertise as needed in the greater Chicago area. And since there isn’t much precedent for diagnosis and treatment in the literature for many of the animals in their care, they practice comparative medicine out of necessity.

As we pointed out earlier, electric eels are technically knifefish. The eel produces its characteristic electrical discharges – both low and high voltage, depending on the purpose of the discharge – via three pairs of abdominal organs composed of electrocytes, located symmetrically along both sides of the eel. The brain sends a signal to the electrocytes, opening the ion channels and briefly reversing the polarity. The difference in electric potential then generates a current, much like a battery with stacked plates.

It is this ability that makes the MRI scan of creatures difficult. According to Vanderbilt University biologist and neuroscientist Kenneth Catania, creatures can vary the voltage of their electric shocks, using lower voltages (around 10 or 12 volts, like a car battery) to sense their surroundings. , navigate and hunt. “They live in murky waters where there is not a lot of light or visibility,” Van Bonn told Ars, which is why they have such small eyes. Eels use higher voltages (100 volts per animal foot, typically ranging between 400 and 500 volts) to stun and kill their prey.

Van Bonn first wondered if he and his staff might not need to worry about these higher voltage discharges, given that aquarium eels are in captivity. Poisonous frogs in captivity, for example, do not produce their trademark poison because they do not need a defense mechanism when in directed care. He tested this by placing a voltmeter in the eel’s aquatic habitat. It recorded a low potential of 10 volts. But when he stung the animal, the voltmeter reading increased dramatically. Conclusion: Eels must be handled with great care.

Electric eels are capable of generating voltages of up to 500 volts to stun and kill their prey.
Enlarge / Electric eels are capable of generating voltages of up to 500 volts to stun and kill their prey.

Clay Harrison / Getty Images

Although an electric eel discharge cannot damage the MRI equipment, it could produce an artifact in the resulting image that would render the image useless. And no one wants manipulators to be electrocuted. The first step is therefore to find a way to anesthetize the eel. Handlers should don latex gloves and non-conductive shoes so that the process interrupts any conductive circuits that may form.

According to Tang, aquarium vets usually put a powder in the water to anesthetize fish, unlike humans, who breathe it in via a gas. Eels breathe air, but they also breathe in water with gills, which is why the team uses the same method as for other fish. The correct dosages must be determined by trial and error, and this reliable voltmeter is in the water to alert the team of any discharge, if the animal is not completely asleep. Once anesthetized, the MRI can be performed as with any non-electric tubular fish or animal.

Additionally, since an anesthetized eel can theoretically drown, vets should administer small puffs of oxygen to the oral cavity. Humans have a windpipe and air passes through it to the lungs so that we can breathe, but electric eels “have this cold, wrinkled tissue inside the mouth,” Tang told Ars. “So all you have to do is blow some oxygen right on the tissue in there.”

The “unhappy triad of O’Donoghue”

Enlarge / “Do knee surgery on a bull frog? Sure, we can do it.”

Maryann Flick / Getty Images

When you specialize in dealing with weird and exotic animals, you are going to rack up some great stories. “Every time we work with one of the animals, we learn something new,” said Van Bonn, such as the time he had to figure out how to perform knee surgery on an American Bullfrog. Whenever the Shedd Aquarium acquires new animals, the creatures are first placed in the quarantine habitat to prevent them from introducing outside pathogens into the carefully controlled environment of the aquarium.

One day an aquarist brought Van Bonn a bull frog that had injured his leg while wrestling with another male of the species. Van Bonn recognized the injury as the frog equivalent of a blown knee. This particular injury, common in human athletes, occurs when there are tears in the medial collateral ligament, medial meniscus, and anterior cruciate. “It means the leg is kind of falling to the side and hanging down,” he said. It is a serious injury, known in literature as “the unfortunate triad of O’Donoghue”.

Human knee surgery is a common practice, and the anatomy is well documented in the medical literature. However, “I didn’t even know if the frogs had a cruciate ligament, ”recalls Van Bonn. “No one writes about the surgical anatomy of a bullfrog’s leg.

He eventually found the necessary anatomical diagram in a 19th century German treatise. Van Bonn also had to build his own artificial frog ligaments from suture material to repair the knee. As for the animal’s anesthesia, it turns out that for some strange reason and despite being overly sensitive to environmental contaminants, bullfrogs need six times the anesthetic to knock them out than fish.

Beluga whales cannot be transported to the hospital from the second floor by elevator.  Their habitat has a secret pool with a platform that can be elevated as needed.
Enlarge / Beluga whales cannot be transported to the hospital from the second floor by elevator. Their habitat has a secret pool with a platform that can be elevated as needed.

What if the animal in need of treatment is larger, say the size of a beluga? The veterinary hospital is located on the second floor of the Shedd Building, and a beluga cannot be carried in the elevator. According to Van Bonn, each habitat in the aquarium also has a behind-the-scenes care area. In the case of the Oceanarium, where beluga whales live, there is a special pool under a building designed to resemble a Pacific Northwest mountainside, with a special platform that can be raised as needed.

But much of the care, such as blood sampling, can be done on site with the help of farm staff. And while there aren’t any instruments specifically designed for beluga whales, commercial horse endoscopes, for example, work just fine.

“There are years and years of experience and training behind all of these unique stories of how to rebuild a bull frog’s knee, or how to build a nebulizer for an anaconda, or what level of pain reliever will help one. shark, “Silk said. Because caring for the Aquatic Menagerie at the Shedd Aquarium involves many unusual cases, team members are dedicated to publishing scientific studies of their work to help develop the literature, disseminating what they have learned. to other zoological and aquatic veterinarians around the world.


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