I've had my male betta for
2 1/2 years, and lately he has spent most of the time at the bottom
in a vertical position, only coming up for air. He is not overfed,
but his fins look shorter. Is it a sign of aging?
Seems to me you must have been a
good mommy to keep your betta for two and a half years. As you know,
bettas on average live about 2 to 3 years. Many die before they hit
2 cause they run into trouble,
Your betta is showing signs of wear and tear.
You mention he is not overfed, so I conclude he is eating. That is a good sign. Once a betta stops eating it becomes really hard to bring him back.
My feelings on this: Your betta is getting older yes, but he also has contracted a bit of a bacterial infection. Fins don't get shorter on their own. Male betta's fins will keep growing throughout the life of the fish. Sorta like our hair, fins grow faster when they are shorter, and when they get to a certain length they almost stop. Any girl who has tried to grow her hair real long will attest to this. Fins never do however get shorter. Unless they get chewed up by another fish or rot away because of fin rot. Granted a betta could blow his fins because of hyperactivity, but from your description I guess this is DEFINITELY NOT the case LOL. So a bacteria is eating away at your betta's finnage. Worry not, it is treatable and you can heal your betta if you act promptly. To treat fin rot, see my detailed instructions and medications prescribed on the disease page under "fin rot". Some photos of the disease will help you compare your betta's fins with that of the ones pictured and see if you can notice a red edge, or a darker edge, which are clear signs of rot. Anywys, in doubt, I always treat. Antibiotics will not hurt your betta, but not treating a fin rot will end up killing it.
Make sure to get the same medication I listed and not anything else. I have tried many and these are the ones that worked best in most cases. Keep the betta's water very clean. If in a jar, consider buying a new jar and move him to it, so you can sanitize the old one. Every time you do a water change, also change the jar and sanatize it again. It seems to help fight the bacteria and promotes faster recovery. Goodluck!