For ID purposes you could do with either an old fish tank to be able to take photos from the side or a large food grade tub that can be partly seen through, some members on here use them as quarantine tanks and you can buy them from the likes of wilkinsons
Both the black markings and the shape of the dorsal fin suggest it's tench. It's too dark for an orfe and doesn't look like a goldfish to me.
If you don't have a tank to take a pic in, get someone to take a pic while you wet your hands and with extreme care lift and hold the fish so a picture can be taken. Grip deliberately, but don't apply any real pressure with both hands. Make sure you're done lifting it out of the bucket and taking the picture in no more than 10 seconds. Unless you can get a proper pic in a tank.
Or after typing that, better still, just google a pic of a golden tench and see if it's this fish! lol