Open up and say “ahh”—some Seattle Aquarium wolf eels just had their checkups!

Just like people, the animals at the Aquarium benefit from expert care, including regular medical exams. And recently, when three of our resident wolf eels were being relocated into new habitats, senior veterinarian Caitlin Hadfield, Vet MB Dipl. ACZM Dipl. ECZM, worked with Aquarium staff aquarists to do routine health checks.

Wolf eel in large cooler filled with water
Dr. Hadfield uses an ultrasound to look at the wolf eel’s body cavity.


Dr. Hadfield uses ultrasound imaging in a variety of ways. Her exams might include elements such as checking the animal’s liver size, determining its sex by the presence of testes or ovaries (and seeing how developed these organs are), checking heart rate and more.

Wolf eel fast fact:

A wolf eel’s body cavity is close to its head. The rest of the animal is muscle. So you could think of wolf eels as relatively small animals with really, really long tails!

Wolf eel being examined by our veterinarian
Dr. Hadfield checks the ultrasound image on the computer screen.


Does the container around the wolf eel look familiar? That’s because it’s a cooler—just like one that you might take camping (or for a really big picnic), but customized for aquatic animal care with an air bubbler. And, completely unlike the water that might collect in your cooler from melting ice, the water in this cooler was pulled from the wolf eel’s habitat.

Close-up of wolf eel head in container
Wolf eel extreme close-up!


The Aquarium is home to 14 wolf eels. Like all animals at the Aquarium, they are closely observed by Aquarium staff every day. The health checks done during the moves are an important part of the veterinary program. “We use these opportunities to check that animals are doing well and to better understand what is normal for each species,” Dr. Hadfield says. “That’s why routine exams are important—especially in a place like the Aquarium, with such a big diversity of animals.”

Wolf eel fast fact:

Even though the experts who care for these animals can tell them apart just by looking at them, they’re also PIT-tagged (PIT stands for passive integrated transponder), just like a microchip on a pet cat or dog.

Veterinarian Dr. Hadfield touches the wolf eel's tail
Checking the tip of the wolf eel’s tail


Just as your doctor might wear gloves during your medical exam, Dr. Hadfield wears them when caring for animals at the Aquarium. “We don’t want to transfer our bacteria and other organisms to the fish, and vice versa,” she says, “because they’re very different.” Gloves also protect the eel’s mucus layer and the skin underneath.

Veterinarians laughing around the wolf eel in cooler
All smiles for a successful checkup!


The checkups for all three animals, a female and two males, were successful and didn’t raise any concerns. “The female was much calmer—the males kept squirming,” laughs Dr. Hadfield. “In fact, the female was calm enough that we could collect a blood sample and look in her mouth.”

Considering their powerful teeth and jaws, examining a wolf eel’s mouth with a hand protected only by gloves could look like a risky choice—but it’s one that Dr. Hadfield made after a lot of observation. “With these animals, I start cautiously and work from the ‘safe’ end,” she says. “I proceed with care, observing the animal’s reactions the entire time. They’re trying to communicate, we just have to understand what they’re saying,” she adds.

Wolf eel fast fact:

The wolf eels Dr. Hadfield examined had average heart rates of about 30 beats per minute. The average for humans is at least double that, between 60 and 100 beats per minute.

*Why were the animals moving into new exhibits? “They’d grown big enough to safely explore new environments,” says Dr. Hadfield. Two of the wolf eels moved from the Elliott Bay window to the Underwater Dome; one moved from the Rocky Reef area to the Elliott Bay window. Look for them the next time you visit the Aquarium!

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