hey guys...just saw this...I had 404 unread emails (no kidding) yesterday to go through with more coming in...and that was AFTER deleting 168!!!
Ok...my expert breeder opinion is a very YOUNG boy! DT long fin. OK...recant that just a bit. Assuming he was one of those baby Betta that petco?smart? sales. He is probably about 3 months old but one of the runts...runts aren't bad!! and doesn't mean he will stay small. In fish, it means that he was last to be pulled out of the grow out by his breeder and all the dominate male hormones have just kept him from growing. Keep his water around 80 to 85*F...82 is best. Feed high protein food (New Life Spectrum Grow Formula) is the best on the market. According to where you get it...it can be expensive though. Feed him as much as he will eat in about a minute, and feed him 3 or 4 times a day (if he gut stuffs...eats a LOT) then only feed 2x a day...IF he gut stuffs, then you can feed smaller amounts 4x a day...(this is my preference). Change 1/2 his water daily for max growth.
Good luck with him!!! He will still grow kinda slow at first, but with in a month, he should pick up some size :D