Yup, what DQ said. I have my two females in a divided tank and one of my females jumped to my other ones side and I didn't realize it until the next day and my big female bit off practically all of my little females fins. They're healing great, but I have no doubt in my mind that my bigger one would've killed my little one if I hadn't seen them. Most people think that the male bettas are the only ones that will attack, but it's not true. Sometimes the females can be more aggressive than males. Some people on here that breed have had their females beat up their male betta.