I had been having problems with my two zebra danio fish so I decided to add a third zebra danio fish to the tank because I read that they behave better in groups of three or other odd numbered groups. One had been bullying the other one, keeping it from the food at feeding time. I also added a Golden killifish to the tank, too. The bully tried to go after the new zebra danio and the golden killifish came to it's rescue, just swimming close enough to make it think twice about bullying the little one. Now the bullying danio fish lets the other ones eat and does a whole lot less bullying of the other danio, staying clear of the smaller one. It's so nice to finally have peace in my fish tank. I would definitely recommend a golden killifish to anyone thinking about getting fish. It also is a real people friendly fish, coming up to the glass and saying hello to me.