I have 6 silver dollars in with some other fish. They are quite large. Sometimes 2 get together and shimmy and shake and put the bit where there anus and sex organs are together. Two started to do this about 2 hours ago and one had a dark black tinge to the edge of its top and tail fins. I rechecked just now and the shimmying and shaking has stopped and so has the black edge. I am guessing it breeding behaviour. Any one any ideas?

I don't confess to be an expert on silver dollars. However, I do know that they prefer quite dim lighting, plants are quite important. Plastic plants are perfectly okay as they will eat live plants. I think the temperature should be fairly warm as well.

I am not trying to breed them. When they do the shimmying thing some of the other fish follow them hoping for a free meal i guess (they must know whats going on its just me who doesnt). I was wondering about the black edge to the top and tail fin