Shedd staff handles electric eelElectric eels (South American knifefish, Electrophorus electricus) can grow to 6 feet long, are coated in slippery slime, breathe air through their mouths and have electric organs over three-quarters of their bodies capable of delivering a 600-volt jolt to anything—or anyone—that threatens them.

When a 4-foot electric eel in Shedd Aquarium’s Amazon Rising exhibit needed a suspicious growth examined and biopsied, Shedd’s aquarists, veterinarians and exhibit fabricators summoned all their technical ingenuity to create equipment and a treatment procedure that would be safe for the fish and for his handlers, too. It was like nothing ever done before at Shedd—or at any other aquarium or zoo.

To address the electrocution hazard, Shedd’s team devised a 4-foot-long, 6-inch-diameter clear acrylic tube with drain holes that would allow them to handle the animal without directly touching him. The tube would also hold the eel in place during the procedure and allow a vet to administer a constant stream of anesthesia-laden water to his gills. The need for nonstop anesthetic was crucial: The eel’s electric organs are controlled by its central nervous system, so as long as the animal is unconscious, the "power" is off.

Aquarists donned long, thick rubber gloves and used nonconductive nets to move the eel from his habitat to a large rubber tub filled with water containing an anesthetic drug for fishes. An acoustic device monitored electrical impulses while a voltmeter hooked up to a computer displayed peak discharges.

Once the animal was considered safe to handle—showing no signs of fin movement or electrical discharges—he was transferred to the acrylic tube. Anesthetic water was pumped across his gills the whole time that he was out of the water. With the eel unconscious, the team took radiographs and weighed him, then biopsied, cleaned and sutured the tumor site in less than 20 minutes.

The biopsy revealed a malignant tumor. Before they could perform surgery to remove the growth, Shedd’s veterinarians needed a magnetic resonance image (MRI) to see the extent of the mass. The eel would have to be transported to a veterinary specialty clinic with full radiological capabilities, located 33 miles from Chicago.

The MRI posed a new set of challenges. During the procedure, the eel would have to be immobile for 40 to 60 minutes, again requiring a constant flow of anesthetic into his gills. But because of the strong electromagnetic field in the room, metal mechanical equipment—specifically Shedd’s anesthesia machine—could not be used near the powerful imaging device. And wastewater would have to be channeled away from the MRI unit and into a drain.

The team designed a new 6-foot acrylic tube to address water containment and drainage, adding Velcro straps and a neoprene lining to better secure the eel. Then they designed and built a metal-free, nonmechanical anesthesia-delivery system that worked by gravity and air pressure to supply water to the fish at the desired constant flow rate.

In addition to the eel in his transport tub, basic life-support equipment and several hundred gallons of water had to be trucked to the clinic. The anesthesia procedure at the clinic was similar to the one at Shedd. The MRI took about 45 minutes. After reviewing the digital images and determining that the eel was stable, the surgeon and veterinarians went ahead and removed the extensive tumor, using a carbon laser, in a two-hour operation. Then the eel was placed in his transport tub to recover in fresh, oxygenated water. When he was breathing well on his own and starting to swim, he was transported back to Shedd.

Having established the handling protocols, Shedd’s veterinarians can now safely give its electric eels routine medical exams, short-circuiting serious health problems in these once-untouchable fish. 

This is just one of the great stories about animal care at Shedd that you’ll find in the new, expanded edition of Shedd Aquarium, the fact- and photo-filled hardcover history of Chicago’s world-famous aquarium, available in Shedd’s gift stores and online.

—Posted by Karen Furnweger, web editor, and William Hana, quarantine manager