A few weekends ago, a woman walked into Aquarium Designs in San Antonio with fish she couldn't care for anymore. The fish were all adopted except for one.

"Unfortunately there was one little goldfish that couldn't seem to keep himself upright. He was stuck on the bottom upside down,” said Derek Burnett, employee.

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The fish has a permanent bladder disorder. It can't float like the rest.

"He's just so tough. He wouldn't give up. I knew I had to do something for him,” Burnett said.

So Burnett adopted the goldfish. He has a background in marine biology, so he tried different diets for the pet, but no luck.

"These type of goldfish, they've been bred a little more than some of the other goldfish. So just like dogs and things that have some of the fancier breeding, you can get a little more health issues that can arise with fish like this,” said Burnett.

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Burnett decided to try to engineer a device that would float for the fish. Using scraps from around the store, he eventually created a goldfish wheelchair.  The fish seems much happier now.

"He went from being upset, stuck on the bottom to be swimming around and zipping around. His tail got to going super fast. This is the happiest I've seen him since we've had him in our possession,” said Burnett.