People cannot rely on what is said about who bettas can and cannot live with. I obviously prove majority of these posters wrong...reason:
15 gal decorated with under gravel filter system / gravel / two filters / heater /
1 fake glow-in-dark plastic grass plant / 1 fake plastic-realistic bush-like plant / 2 silk plants /
1 fake coral reef / 1 rock-plant decoration structure / 4 large river rocks /
1 large gate-cave / 1 small rock-corral-cave /
3 live plants
: [reason for my LOL]
over 10 male and female guppies [obtained from previous boss who no longer had time to care for them; free!]
1 unidentified Pleco / sucker fish
*1 male Viel tail Betta
*1 female Crown tail Betta
the only fish "found" dead due to the bettas were the baby guppies the Betta fish enjoy eating [population control ;D ]
*resided together in a 10 gal tank before moved into the 15 gal tank. Only time the bettas ever fought was after 1st time breeding, and when first put together during feeding time [Blue guarded his feeding floaty]. Sure, they got a sore or two in the little [and I mean little] spats they did get into...which did not last for long. A peck or two, and back to normal. But they recover fast, and only have spats now every "once in a blue moon."
When they bred, as stated by a previous poster, Blue made it quit clear to Red he was no longer interested in breeding, and would chase her away from the nest. Yet I never worried about babies, as Red would always steel / eat the eggs...Blue himself even doing so himself the next day, and she never got hurt in the process as she had plenty of places to "run and hide" [not to mention shes x2 faster then Blue]
Of course, not all bettas are the same, as some are more aggressive. But that dose not mean you cannot put ANY bettas together, ever! that's ridiculous, and not true! Blue and Red now swim together majority of the time...Red shadowing Blue for the most part, until they separate to find baby guppies!
They are my living proof you cannot believe everything you hear about Betta's and what you / they "can or cannot do!" If you want to see if your Betta can live with another...I say go for it! What I did was put a divider between the two of them for about 2 weeks, until they actually started to switch sides. One morning I awoke to find both Red and Blue in the same side together, so figured since they were both fine and alive, I could take out the divider, and they've never separated since.