Can anyone tell me about the lifecycle of the minnow and its breeding habits? I have a small pond and there are six minnows contributed by a small child last year; the minnows have survived and now have changed colour - beautiful green above the dorsal line and a light tan/red below. One, at least has created a nest out of weed and they are now territorial and defending territories, flashing out their fins to show colour and attacking vigorously - amazing to watch. I would love some detail that would illuminate my very amateur observations.
Sounds more like a Stickleback to me. Do these fish have visible 'tubercules' on the head? If so, they may indeed be Minnows in breeding garb. However, I do not know of Minnow territoriality. Good luck.