goldfish spot

[goldene]

I have a large goldfish in a 4 foot glass tank who is 3 and a half years old, he has a red spot only on his tail fin, I don't think it is ancor worms though I have recently fed them live bloodworms and daphnia, he is feeding fine but seems to sit quieter than usual behind the plants, although he comes out as soon as I go near the tank, thinks its feeding time any one have any ideas what the spot could be.

[Cearbhaill]

Red sores that are wounds (red on the outside, white on the inside) are most likely the bacteria Columnaris.
Red sores that are wounds (white on the edge, red in the middle) are most likely the bacteria Aeromonas.
Red dots under the chin or along the back are often a parasite called Costia.
Great Goldfish Link (http://users.megapathdsl.net/~solo/puregold/disease/disease.htm)

[goldene]

Thanks :) Iv taken a look at the link, and :( It does not resemble any of the ones described I am at a total loss it reminds me of a plain pimple spot one without a white head/centre.?