This article is part of our Pets special section on scientists’ growing interest in our animal companions.

Many students begin veterinary school with career aspirations that date back to childhood, when they fell in love with the idea of ministering to cats and dogs, or horses, or the exotic animals at the zoo. Jessie Sanders arrived at veterinary school with a more particular passion. “I was the one weird fish kid,” she said.

It was an interest that had surprised even her. In college, Dr. Sanders had started volunteering at an aquarium, hoping to work with the whales. Instead, she found herself assigned to the fish team — and falling hard for her finned charges.

“I just love fish,” she said. “I love the way they’re built. I love the way they interact with the environment. And there’s still so much that we just don’t know about all the little internal workings.”

Today, Dr. Sanders runs Aquatic Veterinary Services, with patients that include carnival goldfish, pet store bettas and prizewinning koi worth tens of thousands of dollars. Last year, she became one of the first 10 veterinarians to receive a board certification in fish practice, a wholly new accreditation.

Dr. Sanders spoke with The New York Times about life as a fish veterinarian. Her story was based on two conversations, and her responses were edited and condensed.

I’ve done nothing but pet fish for 10 years, and it’s been awesome and challenging. I like the challenge of setting everything in an underwater environment. And the amount of personalities that you get in fish — they have so many little quirks. Some of them are super chill and nice, and some of them are complete terrors.