I'm not sure if this belongs here but I'll ask anyway!

Last fall we moved into a house that abuts a small (1 acre or so) suburban retention pond. It was October and cold so I didn't really notice much in the way of wildlife outside of Canada Geese. I didn't think much could live in the pond because it feeds from storm drain run off and is probably full of pavement and roofing chemicals, and nitrogen from people's lawn treatments.

This spring I was at the shoreline fixing the goose fence, and I saw these two huge fish looking up at me: http://i.imgur.com/Wag0W.jpg

Are these koi? Or carp? They were about 2' long each and looked like giant goldfish.

A few weeks later I heard some loud splashing. The weather was much warmer at that point, and I looked out the window and saw an orange fish briefly jump up out of the water. I thought maybe it was eating something. Then the next day more splashing and I could see them zooming around the edges of the pond, sometimes jumping up like that. This happened every day but only in the mornings, for a couple of weeks and then stopped.

I read this behavior could be flashing which is a sign of illness or poor water quality (I wouldn't be surprised!) I feel kind of bad because there's nothing I can do about it! But, could it be some other reason for the behavior? There are other fish in there - lots of green ones, and some that are bigger than the orange fish. Could they be fighting? Or maybe breeding?

OK, I know this is really vague and not practical because I can't really help the fish if they are sick. But I'm just really curious!

As for behavior...given the time of year, in the am, and near shore I'd guess spawning. Hybrids can spawn but it's thought their eggs aren't viable.