mine went after one another, both about 3inches though, when i got them... I took one back 18hrs later when the store opened and searcehd that day to get a smaller fish... in hope that it wasn't sexed yet and the female, three inch one, wouldn't attack it. They fought so i kept the lights off... the smaller fish wasn't afraid he would float right infront of the others face, i was very nervous... it took part of the dorsal fin off of the little one, just like it did of the biggerone the day before. After 24hrs I decided I couldn't worry about it anymore and I was goign to sell them both back and wait till I found a mated pair or something but the lfs i got them from was closed so i went to a super crappy one that i was never at before and they said they'd give me liike $15 and i laughed and walked away and put them back in my tank.. ever since then they have been really good to eachother... hopefullly mated. I went back to teh lfs i got took the fish back too and he said it died a few days after I brought it back.... which sucks, and i think they hate me now..