Looks like a silver minnow of some kind. Will see if I can find it somewhere. Is a fish that I like if i ever have a big enough tank.
Nice pond, not often do you see so many plants and so clear water in a pond, not around here anyway.
Well after doing some searching it almost definately not a minnow. The tail is far too broad. I would think it might be a hybrid or variant of the bala shark or maybe a female of the species. Wish I could be more help but hopefully someone will know what it is for sure and have a reference.