Callisto was euthanized last weekend because of her ongoing and worsening health condition. It was a tough decision to make, but I think it was the right decision. As many of you know, Callisto had struggled with flipover and floatiness problems for about two years. I had tried to treat with some medications I thought might help and with diet changes, but nothing ever helped. Recently it had gotten to the point where she was obviously deteriorating quickly and she was suffering, so I decided the kindest thing was to end her suffering. After she died, I did a necropsy so I could find out what the problem was internally that caused these symptoms. I ended up finding exactly what I had predicted... her swim bladder was severely deformed.
The normal goldfish swim bladder is comprised of two lobes; the cranial lobe in front and the caudal lobe in back. There is a pneumatic duct, linking the esophagus to the swim bladder, by which goldfish can regulate the air inside the swim bladder. Normally both the cranial and caudal lobe are filled with air, and the cranial lobe is larger than the caudal lobe. Here's a diagram showing a normal goldfish swim bladder.
But Callisto's swim bladder was not like this. Her caudal lobe was completely deflated and shriveled up. Here's a diagram showing what Callisto's swim bladder looked like. So this explains her problems with flipping over and not being able to stay upright in the water. It also confirms that her issue was not something I could have fixed, and euthanizing her at this point was the right decision.
I'll miss Callisto a lot, she was a really special fish. When I first got her, she was super skittish and afraid of everything, but over time she became one of the most friendly and exuberant fish I've ever had. I'm glad that such a fish as her crossed my path, and I hope she was happy in my care. Rest in peace Callisto.