
I've gotta go with koi. In fact I'd bet on it.
I've seen many, many feral koi in my neck of the woods. Sadly, it's a pretty common animal, especially as you get closer to the city. The orange color, in an infinite variety of mixes with black, white, brown etc is standard. I don't know if wild carp throw off colored sports or just lots of people release koi but it's not uncommon to see a few colored ones mixed with the wild variety.
In fact, that's why I'd bet it's a koi in the photo. It's alot easier for me to believe a koi joined in with the crowd of its closest reletives than it is for me to believe a lone goldfish decided to crash the carp party.
