Unidentified fish in my pond

[animartco]

Hi Madelinew,
If it really is six inches long its too long for bullhead, and almost too long for loach. When you said brown grey I immediately thought minnow coloured, though these are also under six inches. If you can see the sides they have a broad back stripe. I agree with the others that a white spot is most likely fungus or damage to the scales. A likelihood is tench, which are very adventurous fish and like exploring for new ponds. In clear water you would be able to see the green colour, but you said it was muddy. Also they hate coming to the surface unless they're chasing something. But as the others suggested a goldfish or other carp is also very likely.