That is a Paradise Fish.
Great fish! They are often found in ponds. People usually put them in ornamental ponds due to the fact that they eat mosquito larva like candy. Pest control!
They are very pretty, very hardy and very easy to keep. They can live in a bowl like a betta as they have a labyrinth lung and room temperature is just fine. They can actually thrive in a bucket of water sitting on the patio. No filter, no heater, no light... just toss in some sort of plant and let them go. They will feed on mosquitos and don't really mind dirty, nasty water. This is the reason that these are actually one of the oldest breeds of fish to be kept as pets. Back in the Victorian error when aquariums were nothing but glass boxes full of water, the Paradise Fish was there. Unfortunately they seem to be vanishing from the hobby. I haven't seen them in the stores for a long time, but next time I do I will buy one.