Andie
Fish Addict
SRC said:Betta's are like PitBulls, some are overly friendly, some are just friendly, some are standofish (no pun intended lol) but not aggressive, some are slightly aggressive, and some are just outright aggressive ...but ALL of them have the capability of severe attacks if "provoked" under the right circumstance..and as an owner you need to be responsible with them.[snapback]852854[/snapback]
That holds true for every dog, really, not just Bull Terriers, Am. Staffs or any of the other dogs often referred to as Pit Bulls Any dog can become aggressive given the right conditions/provocation, and yes, I agree that the same holds true for bettas.
If you absolutely must put something in with your betta, put in something largeish, drab-coloured and short-finned, but I really don't recommend putting anything in at all. The risk to both fish (even the aggressor can suffer damamge if the other fish fights back) isn't anything pleasant to think of. If you want to use up the extra space in your tank, why not make a divider? Then you can put one of any number of other fish on the other side; even another betta, if you choose, and you won't run the risk of a territorial dispute
ETA: hehe oneponygirl posted as I was typing; she's got an excellent pic of a divider, there, and you can find more on this forum and online as well. Happy planning!