At first, Carol Benge and Louie had a pretty good life. Louie is a black-and-silver, three-inch seahorse. He bobbed around Ms. Benge’s fish tank. She fed him tiny brine shrimp.

Then Louie got the bends.

At least, he got the seahorse version of the bends. In September, Louie seemed to have trouble swimming. He moved horizontally and wasn’t acting like his usual peppy self. Small, pearl-like bubbles clustered on his tail.

Ms. Benge guessed the cause: gas bubble disease.

Gas bubble disease happens when bubbles in water get into a fish’s body. It’s similar to a human scuba diver getting a sickness called the bends. The bends happen when a diver comes up out of deep ocean water too quickly.

“I wanted to save my little friend,” says Ms. Benge. She knew she had to act fast.

First, she called a local veterinarian’s office. The receptionist thought Ms. Benge owned a dog or a cat named Seahorse. Nope! These vets did not know how to help Louie.

So Ms. Benge put Louie in a temporary tank. She drove him an hour to the University of Florida College of Veterinary Medicine.

The experts there were curious about the seahorse. They asked if they could do an experiment. They put Louie in a hyperbaric chamber. That’s the treatment for a human diver suffering from the bends. In a hyperbaric chamber, a person (or seahorse, apparently!) breathes in pure oxygen at high pressure. This fresh oxygen goes into the blood. It can fix injured tissue.

Veterinarian-in-training Tatiana Weisbrod gently moved Louie into a Pyrex glass container along with water and a plant from his home tank.

She says, “When he went into the chamber, he was pretty quiet and floating sideways.”

In the chamber, pressure shrank the gas bubbles in Louie’s body over time. Then the veterinarians released the pressure in the tank little by little.

Gas bubble disease is common in aquariums. It often affects seahorses. And now, thanks to Louie, people know how to treat the problem—in seahorses and other fish.

Louie was cured with just one treatment. Now he’s back to munching shrimp from his loving owner’s hand.