i didnt notice that before. its very unsual. a single ray, unconnected to the rest. and there is another one on the opposite side? very strange.
its the equivalent of a minor birth defect, like an extra digit or something. but whether its environmental or genetic i have no clue. if you have time/room, perhaps breed him to a similar looking female (cuz why not preserve the nice caudal and coloration), and then breed one of the daughters back to him. if you dont see any of that in either generation, its likely an environmental accidental occurrence. if you do, and it is likely genetic, that could be a big thing. imagine getting bettas with 3 parallel anal fins, and then eventually getting it to spread to the other fins. a triple finned HM fish, perhaps with some amount of transparcy in the fins so that you can see the other fins flowing through the first one in view, thats something people would pay to own. i suspect more than one breeder would be willing to try and develop such a strain.
Eheim Pimp #296
Canon Pimp #67