Animals

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

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Vets at the Shedd Aquarium in Chicago have devised many unusual procedures to diagnose and treat the animals in their care — including the discovery of magnetic resonance imaging (MRI) of electric eels.
Zoom / Vets at the Shedd Aquarium in Chicago have devised many unusual procedures to diagnose and treat the animals in their care — including the discovery of magnetic resonance imaging (MRI) of electric eels.

Just before Thanksgiving, we reported how the Shedd Aquarium in Chicago solved the strange case of missing chloroquine. An antiparasitic drug was added to the water for new animals in quarantine, but it was mysteriously disappearing. The culprit: hungry, hungry microbes. The post included a throwaway line on how aquarium vets get information on how to give eels electrophoresis and an MRI.

This part seemed to resonate with readers, and we received many inquiries about exactly how this feat was achieved. You asked. We wanted answers. So we turned to Bill van Bonn, the veterinarian in charge of the Aquarium’s Animal Health and Welfare Center, which includes a state-of-the-art animal hospital to monitor the health of all the animals on exhibit and treat them as necessary. Dr. Van Bonn and his colleague, Dr. Carissa Tang, were happy to oblige.

Van Bonn describes the aquarium’s veterinary team as “family practitioners” rather than specialists, although they are able to draw on world-class expertise as needed from the greater Chicago area. Since there is not much precedent for diagnosis and treatment in the literature for many animals in their care, they practice comparative medicine by necessity.

As mentioned earlier, electric eels are technically a knife fish. The eel produces its own characteristic electrical discharge—low and high voltages, depending on the purpose of the discharge—through three pairs of abdominal organs composed of electrocytic cells, located symmetrically on either side of the eel. The brain sends a signal to the electrophysiological cells, opening the ion channels and briefly reversing the polarity. The difference in voltage generates current much like a battery with stacked plates.

It is this ability that makes giving creatures an MRI difficult. According to Vanderbilt University biologist and neuroscientist Kenneth Catania, organisms can vary the degree of voltage in their electrical discharge, using lower voltages (about 10 or 12 volts, like a car battery) to sense their environment, navigate, and hunt. “They live in murky waters where there is not much light or vision,” van Bonn told Ars, which is why they have such small eyes. Snakes use a higher voltage (100 volts per animal foot, usually at between 400 and 500 volts) to stun and kill prey.

Van Bonn initially wondered if perhaps he and his staff wouldn’t have to worry about high voltage discharges, given that eels are in captivity. Toxic frogs in captivity, for example, do not produce their trademark toxins because they do not need the defense mechanism while in managed care. Test this by placing a voltmeter in a water eel habitat. I recorded a low voltage of 10 volts. But when the animal was petted, the voltmeter reading went up dramatically. Conclusion: snakes must be handled very carefully.

Electric eels are capable of generating a voltage of up to 500 volts to stun and kill prey.
Zoom / Electric eels are capable of generating a voltage of up to 500 volts to stun and kill prey.

Clay Harrison / Getty Images

While the eel’s electrical discharge may not damage the MRI machine, it may result in a defect in the resulting image that renders the image useless. And no one wants processors to be electrocuted. So the first step is to figure out a way to anesthetize the eel. Therapists must wear latex gloves and non-conductive shoes in order for the process to interrupt any conductive circuit that may form.

According to Tang, aquarium veterinarians typically put powder in the water to anesthetize fish, unlike humans, who breathe it in through gas. Eels breathe air, but they also breathe through water with gills, so the team uses the same method they use with other fish. Correct doses must be determined through trial and error, and this trusty voltmeter is in the water to alert the team to any discharges, should the animal not completely sleep. Once anesthetized, the MRI can proceed as with any non-electric fish or tube animal.

Also, since a drugged eel can theoretically drown, vets should give little puffs of oxygen over the oral cavity. Humans have a windpipe, and air travels through it to the lungs so we can breathe, but electric eels “have this cold, wrinkled tissue inside their mouths,” Tang told Ars. “So all you have to do is blow the oxygen over the tissue that’s there.”

“The Unhappy Triad of O’Donoghue”

Zoom / “Doing knee surgery on a frog? Sure, we can do that.”

Marian Flick / Getty Images

When you specialize in treating exotic and exotic animals, you will write some good stories. “Every time we work with an animal, we learn something new,” Van Boon said, like the time he had to figure out how to perform knee surgery on an American frog. When the Shedd Aquarium acquires new animals, the creatures are first placed in a quarantine habitat to prevent them from introducing any external pathogens into the carefully controlled aquarium environment.

One day, an aquarist brought to Van Bonn a frog who had injured his leg while grappling with another male of this species. Van Bonn recognized the injury as the frog’s equivalent of a blown knee. This particular injury, common in human athletes, occurs when there is a tear of the medial collateral ligament, meniscus, and anterior cruciate. “That means the leg is just kind of flipping to the side and hanging down,” he said. It is a serious injury, known in the literature as the “unhappy O’Donoghe triad”.

Human knee surgery is a common practice, and the anatomy is well documented in the medical literature. However, “I didn’t even know whether it was frogs or not King “Nobody writes about the surgical anatomy of a frog’s leg,” Van Bonn recalls.

He eventually found the necessary anatomical diagram in a German treatise from the nineteenth century. Van Bonn also had to build his own synthetic frog ligaments from sewing materials to repair the knee. As for anesthetizing the animal, it turns out – for some strange reason and despite the extreme sensitivity to environmental pollutants – that the bullfrog requires six times more anesthesia to anesthetize than fish.

Beluga whales cannot be transported to the second floor hospital via elevator.  Its habitat has a secret pond with a platform that can be raised as needed.
Zoom / Beluga whales cannot be transported to the second floor hospital via elevator. Its habitat has a secret pond with a platform that can be raised as needed.

What if the animal that needs treatment is larger – say the size of a beluga whale? The animal hospital is located on the second floor of the Shedd building, and the Beluga cannot be moved in the elevator. According to Van Boon, each habitat in the aquarium also has a backstage nurturing area. In the case of the Oceanarium, where the beluga lives, there is a private pool beneath an edifice designed to look like a mountain slope in the Pacific Northwest, 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 the breeding staff. And while there are no instruments specifically designed for beluga whales, commercial equine binoculars, for example, work well.

“There are years and years of experience and training behind all these individual stories about how to rebuild an American frog’s knee, or how nebulizers are made for anacondas, or what level of painkillers help a shark,” he said. Tang. Because Shedd Aquarium’s aquatic zoo care involves many unusual cases, team members are dedicated to publishing scientific studies of their work to help build the literature, and to disseminate what they’ve learned to other zoological and aquatic veterinarians around the world.

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