Liquid-Filled Cyst?

Question
Hi, Chris. I've had my pet male Betta, Shi-Zi-Wang since March of last year. He lives in a 2.5 gallon 'Goldfish Starter Kit' type tank, alone. He does not use a filter, and I change the water once/twice a month depending on how soiled it is. I fill the water near the top, but not completely.

My problem is that last night while changing Shi-Zi-Wang's water, I noticed that, right 'inside' his tail fin was a soft, opaque 'ball' of liquid hanging off of the upper side of his tail fin. Upon closer examination while holding him inside his net, I noticed that the cyst-like thing was actually inside his fin, because it was hanging off both sides. We've only just noticed this, and he has been eating and acting normal. Other than that (and his congenitally deformed fins), he looks completely healthy. I could find nothing about this on the Internet, so I hope you might be able to help me with this.

Any input is very much appreciated. Thanks,

Sonja

Answer
Hi Sonja;

Unless it looks infected (red, fuzzy, abnormal) it's probably just as you said, a fluid filled cyst. They are usually harmless and can occur in all types of animals as well as people. (My old 17 year old dog even has one on his hip. The vet isn't concerned at all so I don't worry about it. It happens sometimes.) Just keep his tank very clean so it won't become infected if it ruptures. His water really should be changed weekly. Especially since there is no filter to help keep wastes under control. I know he's been kept under the same conditions for several months now and seemed okay, but the older fish get, the less strong their immune systems are. Clean, fresh water helps the immunity remain strong.

I hope it goes away and he does okay....

At Your service;
Chris Robbins