The one I kept before was in a 10g community that had some guppies. He was quite the character. I remember he would steal food right out of a fish’s mouth if he wanted to. He would also pinch fish if they got too close. It was my mistake for getting him at a time when I was so inexperienced. I noticed 2 guppies had shredded tails and were acting lethargic, but wasn’t sure about the cause. Finally, the the third time around I saw that my dwarf crayfish had grabbed my guppy by his tail and was trying to drag him into a cave. I saved the guppy and rehomed the dwarf crayfish as at the time I was inexperienced and lacked resources for another tank.
The one I keep currently is a female. I only got her because she was kept in the store in a nano tank (I’m not sure the exact size, but it looked to be quite small, maybe 4 gallons) with several small fish (an ember tetra, a cardinal tetra, some type of dwarf danio, and another fish I can’t remember. The tank was awful, but that’s besides the point) and she had been in there for nearly 3 months. I thought she may work out in my 36g community if she was coexisting with these fish, and if not I now have the resources to set up a separate tank for her. She also didn’t seem to be doing too well so I felt bad for her.
I’ve barely had her a month so I can’t say much as to if this will work long-term, but so far she’s been very peaceful. If fish are near her, she will wait for them to move before going her own way. I’ve never seen her pinch a fish or even do a defensive display.
I haven’t owned enough of them to say if gender plays a part in aggression, but I will say it’s all dependent on their personality. Still, they’re great little creatures that are worth caring for