Fish affected by swim bladder disease are unable to control their buoyancy, and may be found floating upside down, leaning to one side side or swimming at the top of the water.

The goldfish in the picture was had swim bladder issues that "prevented it from holding itself upright, and made it permanently stuck at the bottom of its tank," Derek told Buzzfeed News.

Describing his fish-wheelchair, Derek added: “I got some airline tubing that people usually use in their tank and just placed it around the goldfish. I added some valves to the bottom of it, which acted as a ‘chair’ to prop him up.