Popular belief is that fish are dumb as bricks -having no memory, no personality no ability to 'think' the reality is (if you keep fish long enough and observe them) is that they do have memory, can solve 'simple' thought problems and do have their 'personalities'.

Fish can and do react to changes in their life. A school of koi I have in one pond will react and change with the addition of a single fish from the other pond, or the removal of one of the fish.

Recently I inherited 6 new koi, I placed them in the older, larger pond nearly two weeks ago - this morning when I went to feed the fish I noticed that they are still separate from the rest of the fish they have remained in a school of their own.

If your goldfish came from a school it most likely 'misses' its school mates. Being able to see itself it may think it sees another fish. Or maybe it is brighter than average and understands on some level it sees itself.

Concern should only be raised if the behavior of your fish changes or is self destructive, suggestive of underlying illness/disease.

Mirror watching is not a symptom of underlying illness.

No.Some fish are just that good looking.He can't help himself.

Lol! it's thinks there's another goldfish there.

lol,well he is golden.

your fish may not even see its reflection, you dont see a reflection if you look straight on at the glass, only if you look at it from from the corner of the tank or from an angle. Try it you will see what i mean lol :D