So I like to watch and study my betta a lot
, and it seems to me that his caudal fin is either curling or fraying a bit. The very edges look to be a little transparent. His fins just look a bit raggedy to me, but it could just be that he has some crowntail in him with less webbing, especially in the anal fin. I could be over analyzing it all, but if it's early fin rot, I want to be proactive.
Here are some pictures of him, one with flash, three without. PLEASE
don't freak out about the plastic plants you see! They all passed the pantyhose test very well and are really soft. I plan to get silk/live plants as soon as I can afford it!
You can especially see the transparent part on the last pic with the flash.