Originally Posted by Josh
They can be quite aggressive, but like anything its very dependent on the fish. I've had one I've kept in a tropical community tank for a little over 2 years. My grandmother recently bought one for her 20g tropical community and it killed her dwarf gourami and got one or two guppies before she returned it to the LFS
They do have the potential to be aggressive and I think that needs to be taken into consideration.
Both dwarf gourami, and guppies, resemble bettas, so I'm not surprised. Especially if it was a male.