I had a Siamensis (Crossocheilus) in with my Beta and Harlequin Rasboras, but after a few months it began nipping the fins on my Harlequin Rasboras and once in awhile, my Beta too. It seemed to be doing so during the dark night time hours. I finally gave it to my daughter who also has one that has never nipped at her fish. He/she doesn't seem quite as aggressive in her tank, but lately it has nipped the fins on one of them. I originally purchased this fish, because it is supposed to be active, but non aggressive. As well, a great algae consumer, which he/she certainly is! I now have three Oto's and they are wonderful and fun little fish! : )